One of the most popular Sea Dog players returned to Hadlock Field last Friday evening on a rehab assignment from the Boston Red Sox.

Justin Masterson, a right-handed sinkerball pitcher, played in Portland during the 2007 and 2008 seasons before pitching for the Red Sox for two years, then was traded to Cleveland, then St. Louis, before returning to Boston in the off-season last year.

Opening this season in the starting rotation and pitching to a 2-2 record with a 6.37 ERA, Masterson suffered a shoulder injury that landed him on the disabled list.

He pitched for Pawtucket in a rehab appearance, losing while pitching just 1.2 innings and allowing three runs and walking three batters.

Masterson’s 4.2 innings for the Sea Dogs ended with two runs allowed on eight hits, a walk and one batter hit, and two strikeouts. Fifty-two of his 80 pitches were strikes; Portland lost 5-3 to the Bowie Bay Sox.

According to Boston manager John Farrell, Masterson has made a “definite progressive step,” but whether he pitches in the rotation of the bullpen hasn’t been decided.

Following a six-game road trip, the Sea Dogs return to Portland for three games on June 16-18; they take to the road for eight games before coming home for seven games, beginning on June 27.

Sea Dogs third baseman Carlos Asuaje pops up Friday as Portland lost to the Bowie Bay Sox, 5-3.Former Sea Dog Justin Masterson pitches for Portland on Friday during a rehab stint for the Red Sox.