Youkilis has been dealing with the injury for the past couple of weeks, and he said it was not necessarily a byproduct of being hit by pitches from A.J. Burnett on April 25, then Anthony Reyes three days later.
Youkilis clarified that the injury has nothing to do with his back -- the pain is completely in his side.
"It wasn't A.J. -- I got hit in the leg [by Burnett]," said Youkilis. "For a couple of weeks, it's just been tight."
When does the pain manifest itself?
"It just depends on movements," Youkilis said. "Some movements you feel, sometimes you don't feel them. That's about it. There's no rhyme or reason -- check-swing or swing. Sometimes it gets tight and sometimes it doesn't."
Youkilis was not pleased about having just 28 minutes' notice to get ready for Monday's game after both teams endured a rain delay of two hours and 17 minutes.
"I think it's kind of getting ridiculous where, all of a sudden, boom. I don't know if it was an ESPN-type thing, or whatever it was, but that's not a lot of time for the players to get ready for the game in that situation," Youkilis said. "It would be nice to have a little more time, especially when it's pouring down rain when you're going up in the first inning. There just wasn't enough time to start up and heat up."
Though Youkilis wasn't making any guarantees, he was hopeful he'd be back in the starting lineup for Wednesday night's home game against the Indians.
"Tonight, with not being in the starting lineup, hopefully tomorrow, I'll be ready to go," said Youkilis. "That's what you hope for. We'll see. It's just one of those things that you have where hopefully, the body can heal real quick and I'll be ready to play tomorrow."
With Youkilis out of the mix, Red Sox manager Terry Francona moved Jason Bay to the cleanup spot and batted Mike Lowell fifth, while J.D. Drew moved down a spot to the six-hole. Jeff Bailey filled in for Youkilis at first base and batted seventh.
"Joba [Chamberlain] has been having a lot of success against left-handers with that cutter in," Francona said. "We're just trying to have as much balance, knowing Youk is probably not available to hit. We're trying to give ourselves chances where they have to pitch to people, and if they don't, they won't get rewarded for it."
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.