Happ has been sidelined since being hit in the head with a line drive in Tampa Bay on May 8. However, it's been his right knee that's been bothering him, which was aggravated when he fell off the mound after being struck.
Happ has made two starts in the Minors, with his longest outing being five shutout innings with Class A Dunedin on Thursday.
It's likely that the 30-year-old will need two starts at Triple-A before making his return to Toronto.
In seven starts this season, Happ has a 2-2 record with a 4.91 ERA, 1.55 WHIP, .250 batting average against and 26 strikeouts in 33 innings.