Beal has a sore right big toe, while the 38-year-old Garnett will sit out a back-to-back game.
Beal injured the toe during Thursday's loss at Charlotte. Wizards coach Randy Wittman says Beal's injury is ''just going to take some time.''
Beal, who missed the first nine games of the season with a broken right wrist, is averaging 15 points.
Otto Porter will start in Beal's place.
It's the seventh time this season that Garnett won't play the second half of a back-to-back.
Brook Lopez starts instead of Garnett.