Bochy said that he and the team's medical staff want to see how Cain feels Friday before determining whether he'll pitch the next day. Hamstring injuries can linger stubbornly, accounting for the Giants' cautious approach with Cain.
San Francisco's No. 2 starter, Cain is 1-3 with a 3.66 ERA in eight starts. He went on the disabled list last month with a cut on his right index finger, which forced him to miss two starts.
Yusmeiro Petit likely would start Saturday if Cain isn't physically ready.
Chris Haft is a reporter for MLB.com. Read his blog, Haft-Baked Ideas, and follow him on Twitter at @sfgiantsbeat. This story was not subject to the approval of Major League Baseball or its clubs.