Happ suffered a skull fracture and a sprained right knee when he fell to the ground in pain after being struck behind the left ear by a liner off the bat of Tampa Bay's Desmond Jennings on May 7.
Happ, 30, threw a pregame bullpen session on Sunday at Triple-A Buffalo, completing his rehabilitation assignment.
"I feel good," Happ told The Buffalo News. "Obviously I'd like to have maybe finished the last 1-2 starts here a little sharper than I did, but I do feel good about getting pitch counts up and trying to get endurance back. The waiting game was the toughest thing. It's just really exciting."
"He's solid, he's healthy. He threw a lot of pitches [Friday night], but that's what he does," Gibbons told MLB.com.
Happ was 0-2 with a 6.75 ERA in three starts with Buffalo and went 4 2/3 innings in his final start with the team Friday, throwing 95 pitches and striking out six batters. He made five total starts in his rehabilitation stint, which also saw him pitch for the rookie-level Gulf Coast League Blue Jays and at Class A Dunedin.
In seven starts for the Blue Jays, Happ is 2-2 with a 4.91 ERA.
Information from The Associated Press was used in this report.