Oshie took a shot from Detroit's Danny DeKeyser off the outside of his right foot during the third period of the Red Wings' 3-2 overtime win Wednesday night. Oshie limped to the bench but did not miss any shifts and finished the game.
He did not take part in an optional practice Thursday.
The Capitals are already playing without top center Nicklas Backstrom because of rehab from a hip injury. Coach Peter Laviolette said Backstrom has been skating by himself in full gear, adding that the next step is the 33-year-old Swede taking part in a full-team practice in a no-contact jersey.
Backstrom is on long-term injured reserve and not eligible to play until Nov. 6 against the Philadelphia Flyers, though he could be out beyond that game.
Oshie is among Washington's leading scorers with four goals and two assists through seven games. His absence likely means the return of Daniel Sprong against the Arizona Coyotes on Friday night after the winger was a healthy scratch for the Red Wings game.