Astros Make Surprising Last-Minute Lineup Move

"He came in today, he's got a little left leg discomfort," Espada said. "He's seeing the doctor right now, and that's the reason why he's not in the lineup."

Pena will be replaced on Monday by Nick Allen, who returned from the IL on Monday from a left hamstring injury of his own. Allen filled in for both Pena and Carlos Correa earlier in the season as the Astros' Swiss Army knife infielder. The 27-year-old has spent time at second base, third base, and shortstop this year for the Astros.

When he has not been injured, Pena is establishing himself as one of the best young shortstops in MLB. In 48 games this year, Pena is slashing .295/.356/.443, with six home runs, 21 RBI, and eight stolen bases. This season, Pena has a .967 fielding percentage at shortstop, with five errors in 380.0 innings on defense.

The Astros will be hoping that Pena's injury will not require an extended absence from the lineup. Houston has made up some ground in the standings and sits just 0.5 games back of both the AL West lead and the final AL Wild Card spot. Pena's next chance to get back in the lineup will be Tuesday evening in Houston.