The 38-year-old Delgado has not played in the majors since May 2009 for the New York Mets. He has had two hip surgeries since then.
Delgado is set to report to Triple-A Pawtucket on Sunday. He played winter ball in Puerto Rico during the offseason before hip problems slowed him.
Delgado has 473 career home runs.
Delgado worked out for the Red Sox on Friday at Yankee Stadium and manager Terry Francona says he swung the bat well. But Francona cautioned Saturday that it's too early to project what to expect from Delgado.