The rookie goalie was injured during the Flyers morning skate Thursday prior to their game against the Montreal Canadiens, coach Scott Gordon said Saturday. Hart, 20, didn't tell anyone he was injured, then allowed three goals on nine shots before being relieved by Brian Elliott during the first period. The Flyers lost 5-1.
It was the second straight game Hart was replaced by Elliott during the first period; he allowed three goals on nine shots in a 5-2 loss to the Tampa Bay Lightning on Tuesday.
Gordon said Hart met with doctors after practice Friday, when he was diagnosed with the injury.
"Carter to his credit was trying to fight through it (against the Canadiens), and it was a little more severe than he thought," Gordon said.
Gordon said he learned of Hart's injury late Friday after speaking with general manager Chuck Fletcher. By then, Gordon already announced that Elliott would start in goal Saturday, with Hart expected to be the backup.
With Hart unavailable, Cam Talbot, acquired in a trade with the Edmonton Oilers on Feb. 15, will wear a Flyers uniform for the first time as Elliott's backup.
Gordon said in hindsight that the injury could have been the reason for some of the goals Hart allowed Thursday.
"When I look back at the game, forget about the goals," Gordon said. "The shots before the third goal, there were a couple other plays I thought he was a little off on. He just didn't look right to me. Now that might explain itself."
Hart could miss at least five games, including four against Metropolitan Division opponents; the Penguins on Saturday, at the Columbus Blue Jackets on Thursday, at the New Jersey Devils on March 1 and at the New York Islanders on March 3.
Hart is 13-8-1 with a 2.79 goals-against average and .917 save percentage in 22 starts. Prior to his past two games, he was 13-6-1 with a 2.53 GAA and .924 save percentage since his NHL debut on Dec. 18.
The Flyers (28-26-7) entered Saturday eight points behind the Penguins for the second wild card into the Stanley Cup Playoffs from the Eastern Conference.