CHICAGO -- Cubs starter Jameson Taillon exited Sunday's game against the San Francisco Giants with a left hamstring strain after walking the lead-off hitter in the top of the second inning.
Taillon, 34, called for the athletic trainer after throwing ball four to Giants third baseman Matt Chapman. Taillon left a few moments later and was replaced by right-hander Javier Assad.
Assad, 28, was called up from Triple-A Iowa on Saturday after Chicago manager Craig Counsell indicated earlier in the week that he might be needed. It's a possible sign that Taillon was feeling discomfort in the hamstring before he took the mound Sunday.
Taillon, who has made all 13 of his starts, has a 5.19 ERA after giving up a run in the first inning. He also leads the majors in home runs allowed (20).
Taillon's injury is another in a series of ailments for Cubs pitchers that includes Cade Horton (elbow), Matthew Boyd (knee) and Justin Steele (elbow).
Meanwhile, right-hander Edward Cabrera (blister) just came off the injured list Friday, taking the loss in an 18-3 rout by the Giants.
If Taillon has to go on the IL, Assad could simply take his place in the rotation, though Boyd is due back this week after making two rehab starts at Triple-A Iowa.