The discomfort is in the kidney area of Youkilis' back.
"Youk is minimally better," said Red Sox manager Terry Francona.
Youkilis thought he was finally going to make it through a season without going through is annual bout of spasms, but he had no such luck.
"I've had back spasms every year," Youkilis said. "At some point, you get them and they go away. Hopefully it will go away and I'll be good to go tomorrow. It's a long season. Things happen. I get this once a year, this one little thing. I was close to not having it this year and [then] it happened. It's one of those things where it could take just a couple of days and hopefully it's better and makes progress each day."
While the status of Youkilis for Thursday's series finale remains iffy, the Red Sox will get No. 3 hitter Victor Martinez back in the lineup for that one.
Martinez has been in Cleveland the past couple of days dealing with a personal issue, but he informed Francona he can play Thursday.
Without their 3-4 combo, the Sox scratched out a 4-1 victory over the Angels on Tuesday, and Youkilis was confident they could do so again.
"I want to play every day, and I just can't play. It's upsetting to me," Youkilis said. "We're very fortunate in that if one guy is out, it doesn't mean we're not going to win. I've always been a big believer in just one guy out of the lineup doesn't do anything. In order to win, there's a lot of guys in this room that do a lot more on a daily basis, so that's one of my big philosophies."
Facing left-hander Joe Saunders, the Red Sox went with a lineup Wednesday that had Jason Bay batting third, Mike Lowell in the cleanup spot, Rocco Baldelli batting sixth and playing right field and Casey Kotchman starting at first and hitting eighth.
"I think we feel like we'll suit up our guys and try to win," said Francona. "I think we always feel that way. Kotch will play a good first base, and [Saunders is] actually tough on both [lefties and righties]. It's not like he's that much tougher on lefties than righties. He can get righties out, too."
As much as Youkilis hopes to return in short order, he knows that it is out of his hands.
"Once it gets loose, I'll be ready to go," Youkilis said. "After you have [back spasms], you know how to treat it from there on out every day. So you go in and get treated every day and you're fine after that. It's more or less rest, get healthy and play as soon as possible. Once I feel good, I'll be in there. Hopefully it will be tomorrow. If not, the next day."
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.