Some of the best prospects in the baseball could soon be in the Major Leagues with active rosters set to expand from 25 to 40 players on Saturday.
That group could feature several players from MLB Pipeline's Top 100 Prospects list, including some ranked inside the Top 10. Last year's first wave of September callups included Walker Buehler, Alex Verdugo and Francisco Mejia.
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There are, of course, many variables to consider when projecting a possible September promotion: Is the player already on the 40-man roster? Is there an opportunity for him to play or fill a role with the Major League club? Is his Minor League team in a playoff race? Is a pitcher nearing an innings limit?
Here's a list of the top 10 prospects, some of whom have been up previously, who could get called up -- call it part probability, part wish list -- for the final month of the regular season.
Vladimir Guerrero Jr., 3B, Blue Jays (No. 1 on Top 100)
Whether the Blue Jays will call up their 19-year-old phenom in 2018 has been an ongoing discussion for, well, basically the entire season. The chances of it happening this September aren't great, as there's no obvious path for Toronto to offer Guerrero consistent at-bats while also allowing him to continue to develop defensively at third base. Additionally, Guerrero missed a month during the middle of the season with a left knee injury that ultimately delayed his promotion to Triple-A. However, it's hard to rule out a promotion for a guy who's torched Minor League pitching this season at a .387/.446/.643 clip while totaling 19 homers, 27 doubles and 76 RBIs in 90 games.
Eloy Jimenez, OF, White Sox (No. 3)
Having hit .370/.411/.615 in 50 Triple-A games in a season that's seen him establish career highs in most offensive categories, Jimenez has nothing left to prove in the Minor Leagues. A combination of service-time concerns as well as an already overcrowded White Sox outfield could potentially delay Jimenez's arrival until next season. At the same time, the 21-year-old slugger, who's already a member of the club's 40-man roster, stands to benefit from a month in the big leagues alongside other franchise players such as Michael Kopech and Yoan Moncada.

Victor Robles, OF, Nationals (No. 5)
The rise and continued success of teenager Juan Soto has made Robles a bit of an afterthought in the Nationals' outfield. However, the 21-year-old outfielder is still very much a special talent in his own right, with his four plus-or-better tools and knack for impacting games. Triple-A Syracuse failed to reach the postseason in the International League, so expect Robles to see time at all three outfield spots in Washington in September.
Kyle Tucker, OF, Astros (No. 8)
Tucker, 21, has been one of the hottest hitters in the Minors since the Astros optioned him to Triple-A on Aug. 21, hitting for average and power while driving in runs at an obscene rate en route to his second straight campaign with at least 20 homers and 20 steals. He's unlikely to be among the first September callups with Fresno headed for the postseason, but Tucker should be called upon after that to assist Houston in its playoff run.

Jesus Luzardo, LHP, A's (No. 12)
Luzardo has established himself as an elite pitching prospect in 2018 with a meteoric rise through the Minors in his first fully healthy season. The A's would prefer to not call up to the 20-year-old left-hander, who has scuffled a bit at the Triple-A level and is nearing his organization-imposed innings limit of 120 to 125 innings, though additional injuries to an already depleted rotation ultimately could force their hand.
Francisco Mejia, C/OF, Padres (No. 21)
Mejia has produced a .301/.345/.505 in 27 games with Triple-A El Paso, all while starting exclusively behind the plate. The Padres are intent on keeping the 22-year-old switch-hitter at the position, which is where he offers the most real-life and fantasy upside. But with El Paso playoff-bound in the Pacific Coast League, Mejia likely will be among the later callups in September.

Kyle Wright, RHP, Braves (No. 24)
Wright's recent move from the rotation to bullpen at Triple-A Gwinnett suggests that the Braves plan to use their 2017 first-round pick as a reliever down the stretch. He showed in the Futures Game he's not afraid of coming in out of the bullpen in a tight spot if necessary and could serve as either a multi- or late-inning force for Atlanta during the season's final month.
Justus Sheffield, LHP, Yankees (No. 27)
The Yankees have a similar plan in place for Sheffield, who's now made three consecutive relief appearances in Triple-A after previously working as a starter. Throwing strikes has been an issue for Sheffield at times in 2018, but the 22-year-old lefty does have three plus pitches that stand to play up out of the 'pen.
Alex Verdugo, OF, Dodgers (No. 28)
Verdugo was a September callup last year and has since produced a .710 OPS over 29 games in the big leagues, including a .280/.345/.440 clip in 14 games this season. The 22-year-old outfielder is one of the more advanced hitters in the Minors -- a career .310/.367/.445 hitter in over 500 Minor League games -- and surely will be back with the Dodgers in September.
Willie Calhoun, OF, Rangers (No. 47)
Calhoun combines power and patience better than most prospects, and he hit .275/.325/.391 in a four-week stint with the Rangers while filling in for an injured Nomar Mazara. He's a lock to rejoin Texas in September, and he's deserving of a true audition as an everyday player.