"I tried to push off to go tag [the runner], and when I did, I slipped and then it kind of just grabbed," Kelly said.
Kelly stayed in the game, but when he stepped to the plate to hit in the bottom of the second inning, "It just didn't feel right."
Kelly downplayed the severity, but said the medical staff will re-evaluate it on Monday.
"I think I'll be all right," Kelly said. "We're going to treat it tomorrow and then we'll see."
Jason Beck is a reporter for MLB.com. Read Beck's Blog and follow him on Twitter @beckjason. This story was not subject to the approval of Major League Baseball or its clubs.