"We think he needs a little more time," manager Bruce Bochy said of Cain. "He did a light bullpen. He still feels it a little bit. It's not worth the risk."
The Giants do not intend to place Cain on the disabled list, Bochy added.
Cain (1-3, 3.36 ERA) sustained the injury during his last start, resulting in some soreness.
Willie Bans is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.