Lester, who allowed nine runs through 1 2/3 innings of pitching, left the game in the second after signaling to the trainer.
The Cubs breathed a sigh of relief Friday regarding left-hander Jon Lester's injury.
Although he didn't show any physical signs of pain, Lester was scheduled to see the team physician after the game to determine the severity of damage to the large muscle that extends up from the back into the shoulder area.More news: German growth slower, but still strong ahead of election
Even with Lester's rough outing, the starting staff has a 3.28 second-half ERA which is fourth in baseball and they're averaging almost a half inning more a start compared to the first half.
Montgomery is 3-6 with a 3.64 ERA over 96 1/3 innings in 35 games this year, including eight starts. He wasn't the only Cubs pitcher placed on the DL, either - reliever Justin Grimm will also miss time. It was the 11th batter of the inning and he walked off the field.
Lester's nine-run inning Thursday ballooned his ERA to 4.37, but there's no question he's the ace of the rotation and the man the Cubs will be counting on come October.More news: LTFRB allows Uber to file second appeal
Pena has a 4.50 ERA in 16 innings across 10 appearances this year.
Lester gave up 10 runs in two-thirds of an inning at a start versus Pittsburgh on July 9.
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