Conforto, 26, was chasing a popup by Washington's Howie Kendrick when Canó ran into him. The ball fell in for a bloop single.
The Mets did not say if Conforto left with a specific injury. Keon Broxton replaced Conforto in right field.
Conforto had one hit in two at-bats before leaving the game. He hit a three-run home run that tied Thursday's game, 4-4 in the third inning.
Conforto is hitting .271 with nine home runs and 21 RBI in 39 games this season.
Mets center fielder Jeff McNeil left in the third inning. The team cited "abdominal tightness" for the outfielder's departure.
The Mets entered play with a 20-21 record. New York is 3 1/2 games behind the Philadelphia Phillies for first place in the NL East Division.