Per ESPN.com, Mayza was diagnosed with a torn ulnar collateral ligament.
The injury occurred when Mayza threw an 0-2 pitch to Didi Gregorius that completely missed the left-handed batter's box. The southpaw took a few steps off the mound before dropping to his knees and grabbing his arm.
Toronto manager Charlie Montoyo and several teammates met at the mound to console Mayza.
"I love Tim Mayza," Montoyo told MLB.com's Keegan Matheson following Toronto's 6-5 win. "He pitches every day. He's done a great job and he's part of our future. He felt it and it was emotional. Everybody was, because everybody loves Timmy Mayza."
A 12th-round pick by the Blue Jays in 2013, Mayza is in his third MLB season. The 27-year-old had more appearances in 2019 (68) than in the previous two seasons combined (56). He ranks fourth among American League relievers in appearances.
Mayza will finish this season with a 4.91 ERA and 55 strikeouts in 51.1 innings.