Manager John Farrell said before Monday's home opener that Lackey is still in a 48- to 72-hour recovery window and will be re-examined later Monday. Lackey, who left the mound in the fifth inning Saturday in Toronto after injuring the arm, would not be needed until Sunday, due to the team's off day Tuesday.
That start is up in the air, but a return soon thereafter has not been completely ruled out.
"[Starting] on his fifth day, unlikely, but we're not at the point of saying he's a [candidate for the disabled list], either," Farrell said.
Clay Buchholz goes Monday against Baltimore, and after the day off, Ryan Dempster and Felix Doubront finish the series against the Orioles on Wednesday and Thursday. Jon Lester and Buchholz can then go on normal rest Friday and Saturday, but Lackey, or an alternative, would be needed after that.
Farrell said that Alfredo Aceves would be the obvious candidate, which makes Aceves' workload worth watching as the Baltimore series progresses.
There is no reason to believe that the club will take any risks with Lackey. The fact that it's early April is one reason, as is Lackey's long road back from Tommy John surgery. Another factor is the solid stuff that the veteran showed before suffering the strain. The Sox want to make sure they see that again soon.
"A couple of days ago was the first time he's pitched with that kind of intensity in probably two years, and it's not uncommon that you're going to feel some soreness," Farrell said.
"Certainly this was different than just soreness because he came out of the game, but he was getting after it good the other day and not just in terms of velocity, but the action of his secondary stuff. He looked great on the mound. We'll be cautious with this."
Lackey declined to speak with reporters during clubhouse availability before Monday's game.
Tony Lee is a regular contributor to ESPNBoston.com.