Caron Butler left the Mavericks' game against the Bucks on Saturday night in the first quarter with a left knee injury.

The extent of Butler's injury isn't yet known, but Dallas is preparing to be without the forward for an extended period of time.

"We're afraid that it's potentially serious," Rick Carlisle said. "We'll find out [Sunday] where things are at, probably later in the day."

Butler was expected to remain in Milwaukee overnight before returning to Dallas on Sunday.

The Mavericks were already playing without Dirk Nowitzki and Shawn Marion.