Conflicting reports I guess
Rotoworld:
Lester was sent to see Dr. Stephen Gryzlo for a more in-depth exam, and it's possible Gryzlo will determine the injury is more serious. However, at least initially, it appears that the left-hander might not miss too much time. Even in a best-case scenario, a trip to the disabled list is virtually guaranteed. We'll find out more about Lester's condition later Friday. Mike Montgomery will fill in as long as Lester is out. Aug 18 - 9:14 AM
http://chicago.suntimes.com/sports/cubs-jon-lester-leaves-game-with-apparent-injury-in-second-inning/
The Cubs are bracing for the possibility that they could be without their rotation ace for most or all of what’s left of the regular season after Jon Lester left his start Thursday in the second inning because of tightness in his left lat muscle.