Lackey strained his right bicep on April 7 in Toronto. He has been playing catch the last few days and will throw a bullpen session on Friday.
It's possible -- if not likely -- that Lackey will need at least two Minor League starts before pitching for the Red Sox.
"He threw 76 pitches in that first outing, so after two weeks there's going to be about a 10 to 15 percent reduction in total pitches thrown," said Red Sox manager John Farrell. "We'll hopefully get him four innings and 65 pitches. Most importantly, he's testing it at full speed in a game environment so when he does return to us, there's less question in his mind of what he might experience on the mound."
Morales, out with a lower back strain, hasn't thrown a pitch for the Red Sox this season. He threw a Minor League game for Class A Greenville on Wednesday, throwing three scoreless innings.
The plan the Red Sox have for Morales is to stretch him out as a starter, which could take most of the 30-day maximum he has for the rehab assignment.
"We've got a plan to continue to stretch him out," said Farrell. "Now if there's a change in that plan where we would say, OK, we feel like we're in good shape from a rotation standpoint and we shorten him down to get him back to the bullpen, that's an option. We're still looking to stretch him out as a starter."
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.