Pro Bowl running back Jamaal Charles left midway through the Chiefs' practice Monday with what coach Andy Reid called a strained foot. X-rays were negative.

Charles was participating in an 11-on-11 portion of practice pitting the No. 1 offense against the top defense when he walked off the field and spent a moment speaking with trainers. He climbed into a cart and was driven up a long hillside to the locker room.

Dozens of people watching practice tweeted that Charles had been "carted off the field," and that triggered a rush of speculation about the nature or severity of the injury.

Charles missed nearly an entire season two years ago with a torn ACL in his left knee.