Milledge has been on the 15-day disabled list since June 28 with a strained right groin, an injury he sustained while attempting to make a sliding catch in the outfield against the Orioles.
Manager Manny Acta said he expects Milledge to play three innings at the Nationals' Spring Training complex in Viera, Fla, on Sunday.
"He's running the bases, he's ready to start his rehab tomorrow," Acta said.
Milledge, who was acquired from the Mets in November in exchange for Ryan Church and Brian Schneider, is batting .245 with seven homers, 32 RBIs and 13 stolen bases this season for the Nationals.
In the 15 games since Milledge went down with the injury, Willie Harris is hitting .319 (15-for-47) and playing a solid center field.
"He has played well over the past month or so, and the injuries -- he's one of the guys who has benefited from that," Acta said of Harris, who is 7-for-15 over his past five games.
Ryan Lavner is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.