Two of Jason Spezza's five goals this season have come in the past two games. (Sean Kilpatrick/Canadian Press)

The Ottawa Senators lost more than a hockey game on Monday night.

More painful than a 3-2 setback to the rival Toronto Maple Leafs was news that centre Jason Spezza felt something "pop" in his right knee after getting tangled up with Leafs forward Lee Stempniak after a faceoff late in the third period.

The Senators believe Spezza could be sidelined for four to six weeks, according to the Ottawa Sun. An MRI is scheduled for Tuesday evening.

It appeared Stempniak rolled up on Spezza's leg as they battled for the puck. Spezza hobbled to the bench and was helped off the ice.

"I'm not doing too good," he said following Tuesday's practice. "I just felt something pop, kind of. I felt something and then I tried to get up and skate and I had no power."

Spezza has struggled mightily for much of the season but appeared to be breaking out of his slump with goals in consecutive games, including Monday. He has five goals and 19 points in 30 contests this season.

'Great opportunity'

Jesse Winchester skated alongside Milan Michalek and captain Daniel Alfredsson at practice Tuesday as the Senators prepare for Wednesday's date with the visiting Buffalo Sabres.

Ottawa is also without starting goalie Pascal Leclaire, who is nursing a broken cheekbone.

"It means we're going to have to be more of a team than ever," Senators head coach Cory Clouston told reporters. "It's a great opportunity for some guys."

Forward Josh Hennessy has been summoned from Ottawa's American Hockey League affiliate in Binghamton, N.Y.