The Red Sox have summoned Japanese right-hander Junichi Tazawa from Pawtucket to take Melancon's spot on the roster.
"Mark just has to be the pitcher that he is," said manager Bobby Valentine. "He struggled with his command. He's a great command pitcher, and thus far, he hasn't had it. We don't feel that he'd have the opportunity really here to work through it. He was anxious to get an opportunity to work more regularly so that he could get back to where he belongs."
Melancon was shelled by the Rangers on Tuesday, giving up four hits, six runs, two walks and three home runs while not retiring a batter.
The righty has pitched in four games and allowed at least one run in each of them, posting an ERA of 49.50 over two innings.
Even in Spring Training, Melancon never looked in rhythm, though he seemed to be trending that way in late March.
"He was so close I thought, yeah," Valentine said. "I thought as we talked together, his last three outings [of Spring Training] were, none of them were as clean as we really wanted, as he really wanted. Two of the hitters, if he faced three, two of the three, he was throwing the ball right where he wanted. Never quite had the perfect outing. Hopefully he'll have a few of those and put them under his belt and move on."
Last year, Melancon pitched in 71 games for the Astros, fashioning a 2.78 ERA while notching 20 saves.
Tazawa underwent Tommy John surgery in 2010 and pitched most of last season in the Minors.
This year for Pawtucket, Tazawa didn't allow a run in his first four outings, walking two and striking out nine.