Chicago starter John Lackey left the Cubs' game Sunday night against the St. Louis Cardinals with two outs in the seventh inning because of an apparent injury.
With Chicago leading 3-1, the right-hander grimaced in pain after throwing a pitch to Randal Grichuk and the count at 2-2.
Cubs manager Joe Maddon, a trainer and infielders came to the mound.
Lackey walked off the field and was replaced by Justin Grimm, who struck out Grichuk.
Lackey allowed only an unearned run and four hits in 6 2/3 innings and struck out five.