TORONTO -- David Ortiz left Thursday's 8-0 loss to Toronto in the ninth inning with back spasms after he checked his swing on an offering from Blue Jays lefty Rob Rasmussen.
Ortiz came up clutching his back, and he was replaced by pinch-hitter Jonny Gomes.
Red Sox manager John Farrell said Ortiz felt a spasm in his mid-upper back, and he expects the slugger to be sidelined on a "day to day" basis.
"We're still examining him right now. Right now it's day to day," Farrell said.
Farrell said he's doesn't believe the Red Sox slugger has ever experienced a similar injury.
It was an unfortunate end to what had been a productive series for Ortiz, who went yard four times over four games.
In Monday's series opener, Ortiz swatted a pair of dingers -- his 452nd and 453rd -- to tie and pass Hall of Famer Carl Yastrzemski for No. 36 on the all-time home run list.
After going deep again Tuesday, he hit his 37th career homer at Rogers Centre on Wednesday, passing Alex Rodriguez for the most homers by a visiting batter at the stadium.
Ortiz has homered five times at Rogers Centre this year, tying his previous season high for home runs north of the border (2004, '05, '11).
Jamie Ross is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.Less