BOSTON -- Bartolo Colon will officially start his push back to the Red Sox's rotation when he begins a rehab assignment for Triple-A Pawtucket on Tuesday night in a start at Scranton, Pa.

But considering that Colon has been on the disabled list since June 17 with a lower back strain, he won't be rushed through his rehab.

"If you're to take a normal Spring Training progression, you're looking at four or five starts to get him comfortably up to 90 pitches in, hopefully, six innings," said Red Sox pitching coach John Farrell.

On Tuesday, Colon will go two innings, as a starter normally would in his first start of Spring Training.

He threw a side session on Saturday at Fenway Park.

"He threw very well," Farrell said. "[He] threw 50 pitches. We also incorporated almost a simulated inning where he sat five, six minutes before throwing his last 15 pitches. He responded well to that. We've got to build up the endurance in the back and in the overall conditioning, and get him back to game speed."

Before going on the disabled list, Colon pitched well for the Red Sox, posting a 4-2 record and a 4.09 ERA in six starts.

Colon isn't the only Boston pitcher going to Triple-A. Reliever David Aardsma will pitch for Pawtucket on Sunday, exactly 15 days after going on the disabled list with a right groin strain.

How long will Aardsma's rehab be?

"We don't know," said Red Sox manager Terry Francona. "What happened in Anaheim was, he threw out of the bullpen and really felt good. He got in a game at game speed, with adrenaline, and he could feel it. We need to guard against that this time. We just want to make sure he's OK -- get him down there tomorrow and pitch him and see how that goes."