10 Must-Watch Future Stars About to Be Called Up to MLB

The final month of the 2019 MLB season is right around the corner, and with it comes roster expansion from 25 to 40 players.

The bulk of September call-ups consist of players who have spent the season shuffling between Triple-A and the majors—the fringe middle relievers, spot starters, utility infielders and fifth outfielders of the world.

However, at least a few top prospects always get their first taste of MLB action during this window as well.

Francisco Mejia (SD), Victor Robles (WAS), Justus Sheffield (NYY), Alex Verdugo (LAD) and Kyle Wright (ATL) were among the biggest names added to rosters last September.

Which notable prospects are set to crash the party this time around? Let's take a look.

Included is a look at each prospect's spot on the latest B/R Top 50 prospect rankings.

Stats (AAA): .290/.416/.509, 40 XBH (16 HR), 63 RBI, 63 R

Stats (MLB): .294/.365/.510, 12 XBH (5 HR), 13 RBI, 17 R

September Role: Starting first baseman

40-Man Roster: Yes

After posting a .985 OPS with 32 doubles and 27 home runs in the upper levels of the minors during the 2018 season, Nate Lowe impressed in his first MLB action earlier this year.

Despite his solid numbers, the Tampa Bay Rays shipped Lowe back to Triple-A after they acquired Jesus Aguilar from the Milwaukee Brewers at the trade deadline.

Ji-Man Choi has seen the bulk of the playing time at first base this month, and he's hitting .218 with a .762 OPS and two home runs in 69 plate appearances.

It's easy to envision Lowe pushing Choi to the bench in September if he can pick up where he left off. At the very least, he'll provide the Rays with a big bat off the bench.

Stats (Rk/AAA): .303/.396/.606, 20 XBH (11 HR), 31 RBI, 34 R

September Role: Platoon role with C Josh Phegley

40-Man Roster: Yes

The catcher position has not produced much for the Oakland Athletics this season.

Josh Phegley, Nick Hundley, Chris Herrmann, Beau Taylor and Dustin Garneau have combined to hit .238/.292/.404 for a .696 OPS that ranks 19th in the majors at the position.

That could change with the addition of Sean Murphy this September.

The 24-year-old has had a tough time staying healthy in recent years, and a torn left meniscus sidelined him earlier this season.

Since returning to action at the beginning of July, he has nine home runs in 45 plate appearances at the Triple-A level. That offensive production coupled with his highly regarded receiving skills and cannon arm could make him a key contributor down the stretch before he takes over as the primary backstop in 2020.

Stats (A+/AA/AAA): 107.1 IP, 4.19 ERA, 1.35 WHIP, 52 BB, 161 K

September Role: Multi-inning reliever

40-Man Roster: No

The New York Yankees moved Deivi Garcia into a relief role at Triple-A earlier this month.

Whether they did so to limit his innings or as a precursor to a September call-up remains to be seen, but either way, he looks like he's ready to make an impact.

Despite an undersized 5'9", 163-pound frame, Garcia has piled up 161 strikeouts in 107.1 innings this season while climbing two levels to Triple-A Scranton/Wilkes-Barre.

His lively mid-90s fastball and 65-grade curveball would undoubtedly play up out of the bullpen, and the club took a similar approach with Luis Severino down the stretch during the 2016 season.

As the consensus No. 1 prospect in the Yankees farm system, Garcia is a big part of the team's future, but he's capable of helping out now.

Stats (A-/AAA): .263/.332/.415, 42 XBH (10 HR), 55 RBI, 62 R

September Role: Starting third baseman

40-Man Roster: No

The Pittsburgh Pirates have one of the most promising third base prospects in baseball in Ke'Bryan Hayes, and it's only a matter of time before he's manning the hot corner at PNC Park.

The 22-year-old hit .353/.361/.794 with four doubles, one triple and three home runs in 36 plate appearances during spring training, and he appeared to be on the cusp of reaching the majors when the regular season began.

Instead, he's spent the entirety of 2019 at Triple-A Indianapolis, holding his own against older competition and flashing the tools that have made him such a highly regarded prospect.

While he hasn't forced the team's hand with his offensive production, he's MLB-ready defensively and would be an immediate upgrade over incumbent Colin Moran (-12 DRS, -18.9 UZR/150) from that standpoint.

He's ready for a September audition to prove he's ready for the everyday role in 2020.

Stats (Rk/AA/AAA): 60.0 IP, 1.95 ERA, 1.00 WHIP, 23 BB, 59 K

September Role: Spot starter/multi-inning reliever

40-Man Roster: No

Earlier this month, Minnesota Twins assistant general manager Rob Antony told SKOR North that he "would not be surprised" to see top pitching prospect Brusdar Graterol in the majors before the season is over.

The 21-year-old missed time earlier this season with a shoulder issue, which has effectively limited his workload to just 60 innings. Thus, there's no risk of overextending him if he's called up in September and pitched into October.

Armed with a heavy upper 90s fastball, hard slider, slower curveball and developing changeup, he has the four-pitch mix and strong frame to join Jose Berrios atop the starting rotation for years to come.

For now, he would likely slot into the bullpen as a multi-inning weapon, with the potential for a spot start or two if the opportunity presents itself.

Stats (AA/AAA): 132.1 IP, 3.13 ERA, 1.20 WHIP, 59 BB, 170 K

September Role: Reliever

40-Man Roster: No

Last year, the Atlanta Braves included top pitching prospect Kyle Wright among their September call-ups. They also recalled Touki Toussaint and Bryse Wilson, both of whom had made their MLB debuts in August.

In other words, the front office has shown a willingness to promote top prospects as a means of bolstering the pitching staff in September.

Ian Anderson is now the consensus top arm in the system, and after posting a 2.68 ERA with 147 strikeouts in 111 innings over 21 starts at Double-A, he moved one step closer with a promotion to Triple-A in early August.

Wright pitched only six innings over four appearances last September, and the Braves could take a similar approach with Anderson to get his feet wet.

While he might not make a significant impact in 2019, the polished 21-year-old could join Mike Soroka atop the starting staff in the not-too-distant future.

Stats (AAA): .305/.413/.501, 43 XBH (16 HR), 78 RBI, 77 R

Stats (MLB): 5-for-39, 2 HR, 2 RBI, 4 R, 16 K

September Role: Backup infielder and pinch-hitter

40-Man Roster: Yes

The Washington Nationals don't have a clear path to playing time for Carter Kieboom with Brian Dozier and Trea Turner locked in as the starting middle infielders.

That doesn't mean he can't contribute.

While Kieboom fell flat in his first taste of MLB action at the end of April, he went right back to raking upon returning to Triple-A. He's shown a plus hit tool, budding power and an advanced approach with a 14.0 percent walk rate.

Victor Robles was called up under similar circumstances in 2017, and while he saw limited action, he was still able to play his way onto the postseason roster.

Looking at the bigger picture, Dozier is a free agent at season's end, and Kieboom figures to get the first crack at the vacant second base job. Regardless of his role in September, more MLB experience should prove beneficial in the long run.

Stats (AAA): .264/.354/.552, 62 XBH (33 HR), 96 RBI, 90 R

September Role: Oft-used fourth outfielder

40-Man Roster: Yes

Before Yordan Alvarez took the league by storm, Kyle Tucker looked like the next homegrown star ready to break through for the Houston Astros.

The No. 5 overall pick in the 2015 draft was hitting .304/369/.517 with 14 home runs and 66 RBI in 81 games at Triple-A when he was called up for his MLB debut on July 7, 2018.

Expected to make an immediate impact, he instead hit just .156 with 10 strikeouts in 50 plate appearances before he was optioned back to the minors.

He had two more brief stints in the majors, including a September call-up, but he finished with a disappointing .141/.236/.203 line with only three extra-base hits in 72 plate appearances.

While his .264 batting average this season doesn't jump off the page, especially in the offensively driven Pacific Coast League, he's slugged 26 doubles and 33 home runs.

With veteran Josh Reddick hitting .208/.246/.272 in 136 plate appearances since the All-Star break, Tucker has an opportunity to carve out a share of the playing time in right field if he can get hot.

Stats (Rk/A+/AAA): 37.0 IP, 2.68 ERA, 1.03 WHIP, 8 BB, 47 K

September Role: Spot starter/multi-inning reliever

40-Man Roster: No

Jesus Luzardo might have made the Oakland Athletics roster out of spring training if not for a left shoulder strain that wound up sidelining him until June.

The 21-year-old was shelved again in July with a lat strain, and as a result, he's pitched only 37 innings this year after a breakout 2018 season.

With fellow lefty Sean Manaea on the rehab trail, the Athletics don't necessarily need Luzardo to step into a rotation spot. A multi-inning bullpen role makes the most sense considering he hasn't pitched beyond the fifth inning all year.

Luzardo has an electric fastball-changeup-curveball repertoire and excellent command of all three pitches. He's capable of filling a similar role to what Julio Urias has done for the Los Angeles Dodgers this season.

Moving forward, he looks like the future ace of the staff as long as he can stay healthy.

Stats (AA/AAA): .348/.420/.612, 59 XBH (26 HR), 76 RBI, 97 R

September Role: Oft-used utility infielder

40-Man Roster: No

Can the Los Angeles Dodgers really ignore what Gavin Lux is doing at Triple-A?

The 21-year-old is hitting .396/.480/.734 with 18 doubles and 13 home runs in 47 games since being promoted to the highest level of the minors, and he's showing no signs of slowing down.

It would have made sense to call him up when Chris Taylor was on the injured list, but the Dodgers front office opted against it. They might decide not to pull the trigger on a September call-up, either.

However, it's abundantly clear that the 2019 season is World Series or bust for this Dodgers club, and Lux could add another element to an already dangerous lineup.

Recent top prospects Corey Seager and Alex Verdugo both made their MLB debuts as September call-ups, so there is some precedent here when it comes to top-tier position-player talent.

There's nothing left for Lux to prove in the minors, and he should get a real shot at winning the starting second base job next spring. So why not call him up now?

All stats courtesy of Baseball Reference and FanGraphs, unless otherwise noted.