"We're not real concerned at this point," General Manager John Ferguson Jr. said. "He just needs a little more time."
Belfour didn't officially go on the injured reserve list until Saturday, even though he had already been out of action for a while because of a back injury.
The veteran goalie has five shutouts and a 2.17 goals-against average in 44 games.
Backup goalie Mikael Tellqvist made 27 saves in Toronto's 5-4 win Saturday over the Montreal Canadiens.