AL ERA leader Sonny Gray sidelined by back spasms

TORONTO -- Oakland Athletics right-hander Sonny Gray was scratched from his start against the Toronto Blue Jays because of back spasms.

Right-hander Jesse Chavez started against his former team in place of Gray in Thursday afternoon's 4-2 loss. Chavez pitched in nine games for Toronto in 2012. He was charged with the loss Thursday, falling to 6-12 with a 3.84 ERA. Toronto, which has now won 11 straight, leads the major leagues with 615 runs this season. The New York Yankees are second with 534 entering play Thursday night.

Gray, the AL ERA leader at 2.06, first felt sore Wednesday night.

"It was tough not to see Sonny in there," Oakland catcher Josh Phegley said of his All-Star teammate. "We've counted on him all year."

Gray is 12-4 in 23 starts and has lost just once in his past 10 outings.

A's manager Bob Melvin said Gray will not be able to start against Baltimore on Friday, meaning Oakland will have to promote a starter from Triple-A Nashville. Brad Mills, Friday's scheduled starter for Nashville, is considered the leading candidate. He's 3-0 with a 1.56 ERA in three career starts against Baltimore. Ubaldo Jimenez (9-7, 3.79 ERA) starts for the Orioles on Friday.

The Associated Press contributed to this report.