BOSTON -- Boston Red Sox third baseman Kevin Youkilis underwent an MRI on his ailing back, but manager Bobby Valentine said Saturday morning that the results weren't available yet.

Youkilis was placed on the 15-day disabled list on Wednesday, retroactive to last Sunday because of a lower back strain. At the time Youkilis said he thought his back was getting better and that the training staff had figured out what was causing his discomfort. He also said he didn't think it was anything that would require an MRI.

But now the third baseman has had an MRI. On Friday Youkilis said he fully expected to be ready to play again when his time on the DL is up, on Monday, May 14.

Valentine didn't have much else to offer in his pregame media session.

He did confirm, though, that Daisuke Matsuzaka will be ready to make his next rehab start on Monday in Pawtucket. Dice-K, who is recovering from last May's elbow ligament replacement surgery, had been hampered by a sore neck for a few days.

Valentine also said that center fielder Jacoby Ellsbury (subluxed right shoulder) is progressing in his rehab and that Cody Ross has a tender right knee from fouling a ball off the knee during Friday night's game.