The southpaw allowed two earned runs in the 11-2 defeat.
Pomeranz was a All-Star in 2016 and finished last season with a 3.32 ERA, 1.18 WHIP and 186 strikeouts. However, he was much more effective with the San Diego Padres (2.47 ERA and 1.06 WHIP in 17 appearances) than with Boston last year (4.59 ERA and 1.37 WHIP in 14 appearances).
He was also struggling in 2017 before this setback, as he had a 5.23 ERA in his first six appearances.
Boston still has 2016 American League Cy Young winner Rick Porcello and Chris Sale anchoring its rotation, but it could use Pomeranz back and healthy as it chases the New York Yankees and Baltimore Orioles in the American League East.