SAN FRANCISCO — Red Sox right-hander Richard Fitts is on his way to join the club in San Francisco, but that doesn’t mean he’s. a lock to be activated in the coming days.

Fitts, who has been pitching at Triple-A Worcester, will join Boston’s taxi squad on an “if needed” basis, sources said Sunday. The Red Sox are bringing him to the West Coast as insurance because there appears to be a pitcher on the roster who is a candidate to be placed on the injured list. That, however, is a possibility and not a certainty.

Fitts, 25, has a 4.71 ERA in five starts (21 innings) in the majors this year. He made the Opening Day rotation and filled in admirably (3.18 ERA) in a three-start span before suffering a pectoral injury on April 12 in Chicago. His rehab was fast-tracked so he could fill a rotation opening in Milwaukee on May 27, and in his second start back, was tagged for six runs (five earned) in a single inning against the Angels. He was then sent to Triple-A to continue building up and has allowed seven earned runs on 15 hits in 12 innings. He went five shutout innings Tuesday against Buffalo and was scheduled to start for Worcester on Sunday.

It’s unclear why the Red Sox are bringing Fitts west, though a member of the starting rotation might be dealing with a minor injury that necessitates a short IL stint. Brayan Bello got through his outing Saturday fine and Lucas Giolito will pitch Sunday’s series finale at Oracle Park. In Anaheim, beginning Monday, the trio of Walker Buehler, Garrett Crochet and Hunter Dobbins will pitch in the series against the Angels.

Tommy Cassell of the Worcester Telegram & Gazette first reported Fitts heading west.