Schilling, 41, has been rehabilitating an injured right -- throwing -- shoulder since mid-February. He signed an $8 million contract with the Red Sox in November and has said he wasn't injured at that time.
The Red Sox said Schilling's availability depended on his rehabilitation. He isn't expected to rejoin the team before the All-Star break, however.
Schilling was 9-8 with a 3.87 earned run average in 24 starts last season but was 3-0 with a 3.00 ERA in four postseason games. He is 11-2 in 19 career playoff games. Over his career, Schilling is 216-146 with a 3.46 ERA.
The Red Sox filled Schilling's spot on the active roster with right-handed pitcher Lincoln Holdzkom, who has never pitched in the major leagues.