The move was not a surprise, as Byrd was called into manager Bobby Valentine's office after Friday's 7-4 loss to the Nationals.
Byrd was acquired in a trade with the Cubs on April 21 for pitching prospect Michael Bowden, back when the Red Sox were in desperate need of an outfielder after a rash of injuries.
"Marlon came here and kind of saved the day, and now he'll more than likely be with another team. Hopefully, it's not in our division competing against us," said Valentine. "He did a good job while he was here. We just needed room for a starting pitcher today."
The veteran hit .270 with one homer, seven RBIs and a .286 on-base percentage in 34 games for the Sox.
The emergence of left fielder Daniel Nava, the addition of Scott Podsednik and Adrian Gonzalez's ability to play right field made Byrd expendable.
Nava entered Saturday's game with an impressive line of .311/.443/.511 with two homers and 19 RBIs. He made his 28th start in left field since being called up from Triple-A Pawtucket on May 10.
"I guess they're related," Valentine said. "When we got Marlon, there was a real need for outfield depth, and Daniel has filled in very nicely there, he's done a great job."
In fact, the Red Sox chose between Byrd and Darnell McDonald.
McDonald was activated from the 15-day disabled list on Tuesday. In the end, the club's familiarity with McDonald made him the choice to stay.
"He's had a little more history here, obviously -- people and coaches and all were much more familiar with him," Valentine said. "And we feel that he might be able to give us a little more extra-base power when hitting against left-handers."
Matsuzaka made his 2012 debut on Saturday vs. Washington exactly 365 days after undergoing Tommy John surgery. It was the right-hander's first start in the Majors since May 16, 2011, vs. the Orioles.