Happ last pitched in a major league game on May 7, when he suffered a skull fracture behind his left ear and a sprained right knee after being struck by a line drive off the bat of Tampa Bay outfielder Desmond Jennings.
Happ returns to a Blue Jays starting pitching rotation that has struggled mightily in his absence, save for a stretch in June when the team reeled off 11 consecutive wins.
The left-hander was reinstated from the 60-day disabled list on Monday after going 0-2 with a 6.75 earned-run average in three rehab starts covering 13 1/3 innings pitched with the triple-A Buffalo Bisons.
Happ, 31, had posted a 2-2 record and 4.91 ERA in seven starts prior to his injury.
He began spring training without a spot in Toronto's projected rotation, but earned a starting role when struggling left-hander Ricky Romero stayed in Florida to work on his mechanics.
Returning to a major league mound no doubt will be another adjustment for Happ.
It was a frightening scene at Tropicana Field on May 7 when the ball hit by Jennings struck the left side of Happ’s head. The ball travelled to the bullpen in foul territory halfway down the right-field line.
Happ dropped face down at the front of the mound and held his head with his glove and bare hand. He received medical attention for about eight minutes.
Happ remembers releasing the ball.
"I don't remember seeing it," he said. "Just immediate loud ringing in my ear. Just pressure on my ear, and I was on the ground. That was kind of it.
"It took me a few seconds to kind of figure out what was going on, but I do remember them being there … the coaches and Gibby [manager John Gibbons] and obviously the trainers. I was coherent and talking pretty quickly.”
Toronto, which entered play Tuesday last in the American League East with a 51-60 record, designated right-hander Michael Schwimer for assignment to make room for Happ on the 40-man roster.