Stroman tore the anterior cruciate ligament in his left knee while participating in a bunt drill Tuesday at the Jays' spring-training camp in Dunedin, Fla.
Stroman, 23, was coming off a promising rookie season. The right-hander went 11-6 with a 3.65 earned-run average and struck out 111 batters while walking just 28 in 130-plus innings. He was promoted from the bullpen to the rotation on May 31 and made 20 starts.
General manager Alex Anthopoulos said Stroman was "crushed" to learn he's out for the year, and the pitcher tweeted he was "beyond devastated."