Thornton (undisclosed) exited Tuesday's practice on a cart, Nate Taylor of ESPN.com reports.
The reason behind Thornton's exit has yet to be disclosed, but this is a situation to monitor. Thornton has been firmly in the mix for a top-three spot on the Chiefs' receiver depth chart throughout the offseason. If Thornton is to miss time, rookie Cyrus Allen would have an increased opportunity to make an impression on the coaching staff.