Lowell, who battled a strained right hip flexor muscle for more than three months, underwent an MRI earlier on Wednesday. Boston recalled pitcher David Pauley from Triple-A Pawtucket to fill Lowell's spot on the 25-man roster.
"We're going to need to DL him. Obviously we're not going to know today or tomorrow the length of this," manager Terry Francona said. "I think we're all hoping it'll be shorter rather than longer, but how he responds to it is going to be what's meaningful."
Having an oblique strain, according to Kevin Youkilis, is something that is difficult to fully understand unless you've experienced one. Youkilis, who is slated to play third in place of Lowell while Sean Casey moves into the lineup at first, said it affects almost every movement.
"It's something serious, because every little move you make in your core area -- just moving, breathing -- can be a hard time for guys having that injury," Youkilis said. "It goes away over time, but you can't really do anything except let it heal."
Lowell, the 2007 World Series MVP, is batting .270 with 14 homers and 67 RBIs in 101 games. He missed almost three weeks in April with a sprained left thumb but battled through the hip flexor injury and has been a staple of the Sox's starting lineup throughout the campaign.
This type of scenario is why the Sox signed Casey before the season began. With Youkilis batting cleanup and moving from first to third, a position he played throughout his youth, Casey -- and his .353 average -- brings a more than reliable bat to the seventh spot in the lineup at first.
"Putting Casey in, a guy who's hitting .350, a professional hitter, and moving Youk over to third -- that's huge," Francona said. "Otherwise, we have the ability to have [shortstop Jed] Lowrie play third, put [Alex] Cora at short. If we have the lead tonight, we might do that anyway."
Still, it'll be a transition having to navigate through August in a pennant chase without one of the team's most reliable players.
"You're always going to miss Mike Lowell," Youkilis said. "It's going to be tough not having him out here at third base and in the lineup. ... You're never going to have that same guy like Mike Lowell in the lineup."
As for Pauley, who is 13-4 as a starter for the PawSox this season, his Red Sox stint might be short. Given the taxing usage of the bullpen on Tuesday against Texas -- 4 2/3 innings -- Pauley gives the Sox an extra arm if needed.
"We brought David Pauley up to fortify our bullpen," Francona said. "In case something happens, we had a lot of guys throwing a lot of pitches last night. The chances are that after tonight's game, everything going to plan, maybe we'll make another move. But we're going to go one at a time here."
Mark Remme is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.