He allowed four goals on 30 shots in a 6-4 win against the Seattle Kraken on Tuesday.
"We knew he had tweaked something a while ago, a week or so ago, and he aggravated it the other night in our game," Maple Leafs coach Sheldon Keefe said Thursday. "We knew that he was uncomfortable after the game and that yesterday he wasn't feeling a lot better. We sent him for some tests and found out this morning he's going to need some time."
Campbell was 24-9-4 with a 2.65 goals-against average, .914 save percentage and four shutouts in 40 games (39 starts) this season. He played for the Atlantic Division at the 2022 NHL All-Star Game.
Since Jan. 8, he was 7-4-2 with a 4.00 GAA and an .872 save percentage in 15 games, and allowed at least three goals 12 times.
Keefe said he didn't think the injury was the reason for Campbell's recent struggles.
"I don't think it's been around that long," he said. "I don't think that's anything at play. He himself was feeling quite comfortable with where he was at."
Petr Mrazek started and was pulled from a 5-4 overtime loss to the Arizona Coyotes on Thursday. The Maple Leafs play six games in the next 14 days, including against the Buffalo Sabres in the 2022 Tim Hortons NHL Heritage Classic in Hamilton, Ontario on Sunday.
Mrazek is 10-5-0 with a 3.43 GAA and .884 save percentage in 16 games (14 starts).
"I think he's in a good place," Keefe said before the game. "For a guy like him who has been in the league and played a lot throughout his career, now you know you're going to get lots of opportunity. This situation is an exact reason why you go out and sign a guy like Petr to partner with Jack, so here we are."
The Maple Leafs recalled goalie
Erik Kallgren
from Toronto of the American Hockey League on an emergency basis and he allowed one goal on 11 shots making his NHL debut in relief of Mrazek.
Kallgren was 15-8-1 with a 3.02 GAA and .904 save percentage in 26 AHL games this season.
"They really like him down with the Marlies and that he's done a good job there," Keefe said. "His play has been good, but they really like his demeanor and his work ethic. This will be an opportunity for Petr to run with it here, but good chance for us to get to know Kallgren better, for sure."
NHL.com independent correspondent Dave McCarthy contributed to this report
