Ortiz was clearly in discomfort Wednesday morning in the Red Sox clubhouse and was wearing a back brace. He said it started to hurt on the plane ride home Sunday from Tampa, Fla.
"He's sore, but better," Red Sox manager Terry Francona said. "He really wanted to play today, but he woke up this morning and he was pretty sore. He is moving around a lot better."
The Red Sox lost to the Jays 5-4 on Wednesday.
This is the first time Ortiz has dealt with a back issue such as this.
"No. I never have, thank God," he said. "It's a spasm you get out of nowhere. I was feeling OK [Tuesday] and I came in and did my workout, but once I cooled off it hit me again. I told [Francona] about it right before the game."
Ortiz said that when he left the ballpark Tuesday night he felt much better, but he couldn't sleep because of the tightness.
"It started in my lower back and then it went side to side," he said. "I'm feeling all the pressure now in my right side."
Ortiz said he doesn't believe he'll need an MRI.
"There's nothing you can do about it," he said. "Heat, cold and stretch."
Joe McDonald covers the Red Sox for ESPNBoston.com.