Cain was about ready to return from his injury rehab for a left groin strain with Double-A Northwest Arkansas last week when another injury occurred to the same leg.
"In the first inning, I went back for a fly ball and a sharp pain hit my leg, and it kind of started tingling," Cain said. "Something didn't feel right, and they took me out of the game. I flew to K.C. the next day for an MRI, and that's when I found out it was torn."
Cain is taking it slow now, icing the injury, with rehab work ahead of him at the Royals' training facility at Surprise, Ariz.