However, he has made it back from this latest ailment in short order and is eager to take the ball for the Red Sox on Sunday afternoon against the Astros.
"Based on the game pitched [on a Minors rehab assignment], and the bullpen [session] that followed, there's been no symptoms that have reoccurred," said manager John Farrell. "The fact is, when he felt it up in Toronto, I think it was just getting to an arm speed and a velocity that he hasn't experienced in probably two years."
Lackey went 3 2/3 innings in his rehab start at Double-A Portland, throwing 67 pitches.
Obviously he won't be pitching a complete game against the Astros on Sunday.
"We've got an idea with a certain pitch range that he'll approach at some point, and that will be the end of it for the day," said Farrell. "The fact that he got up and down four times his last outing, he was up and down into the fifth inning his first outing. That's kind of the range that we're looking at going into tomorrow. The stress of each of the pitches thrown are going to have some impact on the decision of how deep he can go into tomorrow's game."
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. Jason Mastrodonato is a reporter for MLB.com. Follow him on Twitter @jmastrodonato. This story was not subject to the approval of Major League Baseball or its clubs.