Lester injured his lower left lat muscle during his start against the Blue Jays on July 5.
There will be a steady progression for Lester between now and his start, which will take away the need for a Minor League rehab assignment.
"He'll throw a side [session] tomorrow," Red Sox manager Terry Francona said. "He'll come back Wednesday and throw a pretty significant side and then Friday or Saturday, he'll throw a smaller side. Then he'll pitch Tuesday."
Lester, being the competitor he is, was hoping he could have pitched the first day he was activated, which is Friday night.
"I think he was actually aggravated," Francona said. "He wanted to pitch Friday. So I think that's good news for us that he must feel good. But we need to give him a chance where he can go out and not be stuck on 60 pitches in his first game back."