According to Foxsports.com, which cited two Major League sources in confirming the transaction, the Mets have until 1 p.m. ET on Tuesday to work out a trade with the Red Sox.
If they choose not to do so, they could simply allow Wagner to be claimed by the Red Sox without seeking compensation. The third option for the Mets would be to pull Wagner back off waivers, meaning they would lose the right to trade him for the remainder of the season.
Wagner does have a no-trade clause, though he indicated before Friday's Mets-Phillies game that he'd welcome the opportunity to finish the season with a contender.
"I think that's what every player wants to do, is play on a contender and have a shot to go to the World Series," said Wagner. "Like we all know, I'm not getting any younger and the window's starting to shut. You want to have that chance, and take it if you get it."
Wagner was unaware after the game that the Red Sox were the team that claimed him. When asked about the Sox specifically, Wagner said: "I haven't heard anything. I can't speculate anything because y'all make stuff up."
Wagner made his first appearance since surgery on Thursday night, throwing a scoreless inning and getting clocked as high as 96 mph on the radar gun at Citi Field.
The lefty, as of Friday afternoon, said he hadn't been informed about a claim by the Red Sox or any other team.
"I think yesterday kind of helped the situation, but I haven't heard anything. I'm still just excited about yesterday," said Wagner.
Has he allowed himself to think about switching uniforms?
"I can't," said Wagner. "I've got so much ahead of me right now, I can't think about going somewhere else. Yesterday was a big step, but I've got a lot to work on, a lot to do to get better and help myself."
The Red Sox already have an All-Star closer in Jonathan Papelbon, so Wagner would be used as a power lefty setup man.
By taking on Wagner, the Red Sox would be making a significant financial investment. The veteran is owed roughly $2.7 million for the remainder of 2009, and has an $8 million option for 2010 that includes a $1 million buyout.
The 38-year-old Wagner has pitched for the Astros, Phillies and Mets in his career, posting a 2.40 ERA, saving 385 games and notching 1,068 strikeouts over 819 innings. Opponents have hit .189 against him over his career.
The addition of Wagner would give the Sox yet another weapon in a loaded bullpen that already has the likes of Hideki Okajima, Ramon Ramirez, Daniel Bard, Manny Delcarmen and Takashi Saito working in front of Papelbon.