Lee did not throw a bullpen session as planned Saturday, and general manager Jon Daniels said the club will "probably err on the side of caution" in regard to whether Lee makes his next scheduled start.
"Because there's a little apprehension there, it's probably 70-30 chance that he won't go," manager Ron Washington said before Sunday's game against Minnesota. "We've just got to see how he feels."
Lee played catch in the outfield Saturday and got fully stretched out, but because there was soreness he did not test his lower back by taking the mound. He'll try to throw off a mound Sunday if the back is improved.
"He noted some improvement and said the soreness is primarily over the spot of the injection, which isn't unusual," Daniels said Saturday. "He said he'd like to start Tuesday. We haven't made that decision, but we'll probably err on the side of caution. The important thing is we get this behind him so it's not a problem later in the season. And we will, it's just a matter of the timing."
If Lee can't make his scheduled start Tuesday in Toronto, Rich Harden and Scott Feldman are the two leading candidates to replace him. Feldman is scheduled to start as part of a rehab assignment Sunday, but could be held out of it if he is needed. Harden was recently moved out of the rotation in favor of Derek Holland, who gave up four runs in 6 1/3 innings in a 4-3 loss to the Twins on Friday.
Lee complained of back discomfort after another struggling start last Tuesday in Kansas City.
He flew back to Texas and was examined by team physician Keith Meister, who didn't find any structural damage to the back. Lee received a trigger-point injection designed to help relieve inflammation of the muscles. He said Friday that he was sore but thought that could be more from the shot than anything else.
"I can pitch with it and I have been pitching with it," Lee said Friday about the discomfort. "But I want to go out there and be me. Go out there and locate pitches and be more consistent with location and I just haven't been. I think this is a big reason why.
"It's affecting my ability to stay down in the zone and I'm not able to finish pitches as well as I've been."
Lee, who is 0-3 with an 8.28 ERA in his last five starts, said his back has bothered him for a few weeks and acknowledged that he should have said something to the club earlier.
"I want to go out there and compete and help the team win," Lee said Friday. "It's easy to look back and say you should have done this and done that. I wish I had said something sooner. I wasn't really helping the team going out there and giving up six, seven runs a game. I never anticipated doing that either."
He said he's going to try to throw a bullpen session on Sunday. He wouldn't commit either way as to whether he thought he'd make his start Tuesday.
"I don't know," Lee said. "We'll see how it goes. It felt better today and I did some long toss. We have to wait and see what happens tomorrow."