But at the last moment, just when both sides thought there would be a deal, talks collapsed over an apology, according to multiple sources familiar with the situation.
About two weeks ago, Mankins and his agent Frank Bauer arrived at the Patriots training facility in Foxborough, Mass., with both sides intending and believing they would be able to hammer out a long-term deal similar to the seven-year, $56.7 million contract that Pro Bowl guard Jahri Evans signed with New Orleans in the spring.
Shortly before the deal could be consummated, the Patriots asked Mankins to apologize to Patriots owner Robert Kraft for comments he made in June, questioning the New England owner's integrity. Mankins did. He called Kraft, apologized and explained why he spoke out in the way he did. It was a nice conversation and it paved the way for Mankins' long-term deal to be consummated.
Then, about 90 minutes later, just before finalizing the deal, the Patriots requested Mankins issue a public apology. Not only did Mankins refuse, but he became offended, according to sources. The optimism that had been built, the momentum that the talks had generated, completed collapsed -- and even regressed.
Now Mankins no longer wants to play in New England, and the Patriots may be forced to trade him with no resolution in sight.
In an appearance on a radio pregame show, Patriots president Jonathan Kraft acknowledged that Mankins called owner Robert Kraft to apologize privately for his previous remarks on Kraft, but did not elaborate on the details of this report, saying he had not read it.
Kraft did say that the Patriots offered Mankins a contract that "compared to the other top guard contracts stacks up favorably." The sides have a difference of opinion, however.
Kraft said the team would still be open to having Mankins return on his restricted free-agent tender offer. Mankins has refused to sign his $3.26 million tender offer from the Patriots.
"We'd love to have him back," he said. "He's a great football player."
Mankins, a two-time Pro Bowler, would have been an unrestricted free agent under the rules of the last collective bargaining agreement. However, when the owners opted out of the deal, triggering 2010's uncapped year, only players with six years in the NFL gained unrestricted status.
A trade will not be easy. Any interested team would have to satisfy the Patriots' and Mankins' wishes for compensation. One might be easy; two would be extremely difficult.
Adam Schefter is ESPN's NFL Insider. ESPNBoston.com's Mike Reiss contributed to this report.