Red Sox place Kevin Youkilis on DL

The Red Sox have placed third baseman Kevin Youkilis on the 15-day disabled list because of a strained back.

Boston made the move Wednesday and also promoted Triple-A prospect Will Middlebrooks to take Youkilis’ roster spot.

Youkilis had been a late scratch the past three days, and manager Bobby Valentine said he has improved but wouldn’t have been able to play for at least another four days. He last played Saturday night in a 1-0 win over the Chicago White Sox.

Middlebrooks was hitting .333 with nine homers and 27 RBIs in 24 games with Pawtucket.

Valentine also said Josh Beckett would miss his next start Saturday because of soreness in his right side and Aaron Cook would be placed on the roster and pitch in his place. Cook, who had an opt-out clause if the team did not recall him soon, went 3-0 with a 1.89 ERA in five games with Pawtucket.