Maple Leafs coach Sheldon Keefe also told reporters on Wednesday that defenceman Rasmus Sandin will be out "weeks" with a knee injury suffered Saturday against the Nashville Predators.
Mrazek will start in a game that will also see the Maple Leafs debut of trade-deadline acquisitions Mark Giordano and Colin Blackwell, both of whom were obtained in a blockbuster deal from the Seattle Kraken on Monday.
And if that isn't interesting enough, the Leafs will also be wearing their recently revealed reversible third jersey, designed by Justin Bieber's drew house.
In 51 games this season, Sandin has five goals and 16 points while averaging a career-high 16:58 of ice time.
Mrazek, 30, is 10-6-0 this season with a 3.48 goals-against average and an .884 save percentage.