Breaking News: Mariano Rivera carted off

Mariano Rivera was just taken off the field at Kauffman Stadium on a cart after apparently injuring his right knee while shagging flies during batting practice.

Witnesses said Rivera was "writhing in pain'' after the injury, which may have occurred from running into the wall after a long fly.

The Yankees have issued no official information yet, but from the vantage point of the press box, Rivera appeared to be smiling as he was driven off. Trainer Steve Donohue was on the cart with him.

Keep clicking here for the latest details as they become available.