The Toronto Blue Jays' high-powered offense caught a break Thursday that they probably didn't need.

Oakland Athletics ace Sonny Gray was scratched from Thursday's series finale in Toronto hours before first pitch due to back spasms. Manager Bob Melvin told reporters that Gray's condition worsened Wednesday and that it's unclear when the right-hander will return to the rotation.

"He had some back spasms last night and was working hard to get them out of there. ... We'll see how he feels (this weekend) in Baltimore, and we'll get him in there when we feel it's the proper time to get him in there, but at this point, not sure," Melvin said.

Gray, a first-time All-Star this season, entered his scheduled start with 136 strikeouts in 161 2/3 innings and the lowest ERA (2.06) and WHIP (0.96) in the American League.

Right-hander Jesse Chavez started in Gray's place opposite Blue Jays lefty Mark Buehrle.

Toronto is seeking its 11th straight win after taking sole possession of first place in the AL East following Wednesday's 10-3 victory.