The left-hander was scheduled to start against the Boston Red Sox on Saturday night, but manager John Farrell said before Friday night's series opener that an MRI and a CAT scan showed the fracture after X-rays were negative. Farrell said he wasn't sure how the injury occurred.
Happ had been a solid starter since being obtained on July 20 in a 10-player trade with the Houston Astros. He was 3-2 with a 4.46 ERA and 46 strikeouts in 40 1/3 innings with Toronto. In his last start, Happ struck out nine in five innings in a 4-0 loss to the Baltimore Orioles on Monday night.