Couture and St. Louis’ Vince Dunn collided and went into the boards with 12:27 remaining in the period.
Couture, in his 11th season, was favoring his left knee, which he banged into the boards.
He leads the Sharks with 36 points — 14 goals and 22 assists.
“It’s big-time concerning, even if it’s just a couple games or whatever, if it’s a couple weeks,” San Jose coach Bob Boughner said. “He’s a catalyst of our offense, penalty kill and everything. It’ll be a tough loss but hopefully it’s not too long and it’s a day-to-day thing, so we’ll have a better idea about that [Wednesday]. When a guy like that goes down, everybody is very shocked.”
Couture has a walking boot on, Boughner said.
“I know they did X-rays,” Boughner said. “I believe they’re negative, but we’re going to reassess him again [Wednesday].”
The Associated Press contributed to this report.