Valentine said he doesn't know if Beckett will miss a full turn in the rotation or will be slotted in against the Texas Rangers on Tuesday or Wednesday. The manager said it was still "nebulous" whether Beckett would go on the disabled list but said it wasn't likely.
Beckett is 0-2 with a 4.50 ERA against the Rangers this season. The right-hander went seven innings on July 25 in Arlington, Texas, allowing nine hits and four runs in a 5-3 loss.
Beckett was removed from Tuesday's game against the Detroit Tigers with two outs in the top of the third inning after suffering back spasms while pitching on a wet mound at Fenway Park.
Morales made his last start July 13, allowing two hits in five scoreless innings against the Tampa Bay Rays. He made five starts for the Sox while Clay Buchholz was on the disabled list with esophagitis, and was impressive, going 2-1 with a 3.42 ERA while walking eight and striking out 31 in 26 1/3 innings.
With the Red Sox down to just one lefty in the bullpen (Andrew Miller), Morales was returned there. But with the acquisition of Craig Breslow, the Sox now have the flexibility to reconsider returning Morales to the rotation on a full-time basis, especially with right-hander Aaron Cook struggling.