Spezza suffered a left knee injury in Thursday night's 4-2 loss to the Tampa Bay Lightning. The 23-year-old was checked into the boards by Lightning forward Martin St. Louis with six minutes left in the game and did not return. Spezza walked with a noticeable limp Friday morning and there is no timetable for his return.
"I'm definitely frustrated," Spezza told reporters. "The back's starting to feel better. One thing starts feeling better and this happens. But it's part of the game."
He said he didn't know how long he'd be sidelined.
"I've never really had knee injury so I have no idea," he said.
Senators head coach Bryan Murray said Spezza's absence would be difficult to overcome.
"It is frustrating, obviously," said Murray. "You lose a guy like Jason that is a key guy on our hockey team as far as getting points, running the power play, things of that nature."
Spezza was off to a blistering start for the Senators, leading the team with 44 points (19 goals, 25 assists) in 36 games. The 19 goals are just three short of his career high set in 2003-04, and he ranks eighth in league scoring.
The Senators have been beset with injuries this season, losing several key players like forward Daniel Alfredsson and defencemen Wade Redden and Joe Corvo earlier in the year.
Spezza said the hit was harmless, and Murray agreed.
"It was just a bodycheck," said Murray. "It's a freaky thing. I'm not sure how he caught his leg."
Mike Fisher took Spezza's place on the top line in Friday's practice and he's expected to skate with Alfredsson and Dany Heatley for Saturday afternoon's game against the Philadelphia Flyers.
The Senators (17-18-1) sit 12th in the Eastern Conference, and have scored just five goals in their past four games (1-3-0).