Youkilis will serve as the PawSox's designated hitter and get three at-bats. He then will play the field on Thursday for Pawtucket before a final decision is made whether he will rejoin the Red Sox in Philadelphia on Friday.
Youkilis was placed on the 15-day disabled list on May 2 (retroactive to April 29) and was eligible to be activated on Monday.
On Sunday, Youkilis began taking ground balls and was able to swing the bat and continue that routine for the past three days.
"He looked really good taking his ground balls," Red Sox manager Bobby Valentine said. "He was moving around today with a bounce in his step. He'll start tomorrow and get him enough, whatever it's going to take to have him say that he feels good."
Since Youkilis has been sidelined, rookie third baseman Will Middlebrooks was called up from Pawtucket and entering play Tuesday had hit .304 with four homers and 13 RBIs in 11 games for the Red Sox.
The rehab assignment is crucial because rival officials feel that if the Red Sox are going to recoup some trade return for Youkilis, he needs to get back on the field for an extended period of time and demonstrate he's healthy.
Youkilis' contract runs through the end of this season, and he could have trade value to a team such as the Dodgers or Reds -- if he can show he's healthy enough to be productive, baseball sources told ESPN The Magazine's Buster Olney.
"Right now, I can't see another team giving them anything for him," a GM told Olney on Tuesday morning. "There are too many questions about what he's got left in his body."
Information from ESPN The Magazine senior writer Buster Olney was used in this report.