Youkilis was reinstated to the active roster after missing 22 games due to lower back stiffness. He takes the roster spot of outfielder Cody Ross, who was placed on the DL with a broken foot bone.
The 33-year-old Youkilis was batting .273 with two home runs and nine RBI before playing his last game April 29.
The Red Sox placed outfielder Ryan Sweeney on the seven-day concussion disabled list Tuesday. He was injured Saturday while diving to make a catch against Philadelphia.
Sweeney is batting .311 with 14 doubles and 12 RBI in 34 games this season.
Scott Podsednik was promoted from Class AAA Pawtucket to bolster Boston's outfield ranks.