Pomeranz was pulled from Friday's game against St. Louis with forearm tightness, Michael Silverman of the Boston Herald reports.
"Forearm tightness" is sometimes the initial diagnosis made public before an eventual Tommy John surgery. Pomeranz suffered a late-season drop in velocity in 2017, a common indicator of an impending serious arm injury, so there's some concern here even though it's way too early to know for sure. The exact severity of the issue won't be clear until further tests are performed.