Beal was driving to the basket on a fast break when he he slipped and fell in the lane, ending up underneath the basket.
He was able to get to his feet and walked unaided to the locker room. He did not return to the game.
Beal scored five of Washington's 20 first-quarter points. The Wizards went on to lose, 103-101.
"Brad goes down; we have to have some of our other guys step up,'' Washington coach Randy Wittman said. ``Sugarcoat it all you want, we have to have other guys step up and play.''
The Wizards' shooting guard has already missed 18 games this season.
Information from The Associated Press was used in this report.