"Obviously it's a possible DL, but we're going to wait for the results [of the MRI]," Giants manager Bruce Bochy said. Bochy added he felt "concerned" and compared Cain's latest injury to a similar one in May 2014, when Cain went on the 15-day disabled list and missed two starts.
"That's a tough break for him, particularly the way he was throwing the ball," Bochy said of Cain, who entered the game with a 1.71 ERA in his previous three starts. "He was locked in with his pitching. So it's a setback, but we'll know more tomorrow."
Cain did his best to remain optimistic, noting this hamstring strain is in a higher spot than his previous one.
"Hopefully we caught it early enough to where it won't be a big deal," Cain said.
Should Cain miss a couple of turns in the rotation, the likeliest candidates to replace him are Albert Suarez, the rookie right-hander who relieved him Friday and pitched five innings, and Chris Heston, last year's No. 5 starter whose performance for Triple-A Sacramento has improved lately.
Suarez yielded three runs and absorbed the decision, but he spared other members of the bullpen from spending themselves physically at the outset of a 10-game trip with two potentially grueling games remaining here.
"He did a nice job for us. He stepped into a tough situation and kept us in the game," Bochy said, adding Suarez "obviously" would be in line to start.
Heston has recorded a 2.70 ERA while striking out 22 in 23 1/3 innings in his last four starts for Sacramento.
Cain said he initially noticed discomfort when he threw his next-to-last pitch to Gerardo Parra, the final hitter he faced in his 1 2/3-inning stint. He stayed in for one more pitch, hoping that what he felt simply would go away. After Parra flied out, Cain was immediately surrounded by Bochy and head athletic trainer Dave Groeschner, who could tell something was amiss.
"Sometimes you get stuff to kind of release," Cain said. "You know your body pretty well. I was kind of hoping that maybe it was something that would release and not be a big deal. But when Gresh and those guys came out there, you could tell [the hamstring] was starting to get tighter and tighter. If I stayed out there, I would have made it worse."
Cain acknowledged the potential of going on the shelf was discouraging. But, he said, "The biggest thing is to try to get better and not sit here and worry about it."