Workman seemed fatigued of late, which is why Ranaudo, who is ranked the club's No. 6 prospect, started at Cincinnati on Wednesday.
With Ranaudo going back down, Alex Wilson was recalled from Triple-A to give the Sox another reliever.
Wilson spent much of last season with the Red Sox. He has pitched in three games for Boston this season, posting a 3.38 ERA.
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.