The Capitals said Monday that the two-time league MVP suffered an "upper-body strain" in Sunday's overtime loss to Columbus.
Ovechkin had an MRI and will travel with the team while receiving treatment.
Ovechkin has missed only four games -- and just two because of injury -- since coming to the NHL in 2005. He sat out once during his rookie season with a groin injury and couldn't suit up for one game last season because of a bruised heel. He also missed two games last season to be with his ailing grandfather in Russia.
If Ovechkin is out a week, he would miss three games: Wednesday at New Jersey and home-and-home against Florida on Friday and Saturday. He led the league in goals (14) and points (23) through Sunday's games.
"We have to buckle down," coach Bruce Boudreau said. "You look at a goal a game he scores. We've got to play better defense. We can't allow four and five goals a game. You have to win 3-1 and 2-1 and, if you get lucky, sometimes make it a 4-2 game. I think we have enough character players who understand what we will have to do without Alex."
Ovechkin appeared to hurt his left shoulder or left arm during a second-period scrum that started when he was bumped by Jason Chimera. Ovechkin responded with a shove, and players from both teams quickly joined in.
Ovechkin stayed in the game, but later in the period became tangled with Raffi Torres and fell to the ice. He got up grimacing and gingerly skated directly to the locker room.
The Capitals did not practice Monday, although Ovechkin was at the practice facility for treatment.