Keenum is expected to get the opening-game nod against the Philadelphia Eagles over rookie first-round pick Dwayne Haskins.
Redskins head coach Jay Gruden said Sunday that Colt McCoy - who many thought could compete for the job - may not return until "two or three weeks" into the season as he recovers from the leg injury that ended his 2018 campaign, Schefter adds.
Keenum has started each of Washington's first two preseason games, completing 7-of-16 passes for 112 yards and one touchdown in limited action.
Haskins, meanwhile, has shown flashes of what made him the No. 15 overall pick in April.