Zubrus was replaced by rookie forward Drew Stafford, who played for the first time since Game 4 of Buffalo's second-round series win over the New York Rangers.
Zubrus has been nursing the injury since Game 1 against Ottawa, and played just four minutes in a 3-2 win in Game 4 on Wednesday.
The Senators also made a change, welcoming back right-winger Patrick Eaves, who missed 11 games because of head injury. Oleg Saprykin, who scored the winner in Game 1 against Buffalo, was forced to sit.
Zubrus has eight assists in 15 playoff games, and played a key role in shutting down both the New York Islanders' and Rangers' top scoring lines in Buffalo's first two series victories.
Stafford has played in nine playoff games this post-season, totalling four points. He finished the regular season with 13 goals and 27 points in 41 games.