Mrazek was pulled from a 5-4 overtime loss to the Arizona Coyotes on Thursday.
"Ultimately, for us, when we look at it, there are a number of different things," Toronto coach Sheldon Keefe said Friday. "You want to give Petr an opportunity to get back in and respond. There is the fact that there is an outdoor game and you have that happening, Petr has experience playing outdoor games in the NHL.
"There is a lot of stuff going on there that makes it obvious to us to give Petr another chance to go back in. There is the simple fact that he has won 10 games for us this year. He hasn't played nearly to his ability, but he has won games for us this season. We need to win a game on Sunday."
The Maple Leafs will play the Buffalo Sabres at Tim Hortons Field in Hamilton, Ontario (4 p.m. ET; TNT, SN, TVAS, NHL LIVE).
Maple Leafs goalie Jack Campbell is
out at least two weeks
because of a rib injury, and backup Erik Kallgren made his NHL debut Thursday in relief of Mrazek, who allowed four goals on 12 shots playing 31:57.
"Kallgren showed very well. He showed us that he can go in for us if we need him to," Keefe said. "We like a lot of what he did last night. He didn't get a lot of work -- eight shots, or whatever it was (one goal allowed on 11 shots) -- but it shows for our players what they can do for goalies with their work. That is on us to continue to do that for Petr."
Campbell allowed four goals on 30 shots in a 6-4 win against the Seattle Kraken on Tuesday. He is 24-9-4 with a 2.65 goals-against average, .914 save percentage and four shutouts in 40 games (39 starts) this season.
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.
"We knew he had tweaked something a while ago, a week or so ago, and he aggravated it the other night in our game," 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."
Mrazek is 10-5-0 with a 3.43 GAA and an .884 save percentage in 16 games (14 starts). He played outdoors for the Detroit Red Wings against the Colorado Avalanche in the 2016 NHL Stadium Series at Coors Field in Denver and made 24 saves in a 5-3 win.
"Petr came in today and had a good workday," Keefe said Friday. "The reports were all really good and positive. That was kind of the last thing I was looking for towards making a decision for Sunday.
"There were so many signs, in particular with it being an outdoor game, that I don't want to put Kallgren in that spot, especially when we have a guy who does have experience and has a little something to prove on Sunday."
NHL.com independent correspondent Dave McCarthy contributed to this report
