Logan Mankins refused to take a pay cut to remain with the New England Patriots, according to a league source.
Mankins was traded to the Tampa Bay Buccaneers on Tuesday, with tight end Tim Wright going the other way.
According to NFL Media analyst Ian Rapoport, the Patriots asked Mankins - who was due over $20m (£12m) in the next two years - to reduce his wages.
When the two parties failed to reach a conclusion, the franchise made him available and the Buccaneers snapped him up.
Rapoport revealed via Twitter: "Why did the Patriots end up dealing Pro Bowler Logan Mankins? They asked him to take a pay cut. He refused (as you'd expect). Then became available.
"Bucs called about acquiring a Patriots backup guard. They were surprised to get Mankins."
Patriots coach Bill Belichick labelled Mankins as the best guard that he had ever coached following his move.
