Two people familiar with the deal told the Associated Press on Tuesday that the Philadelphia Eagles have agreed to trade McCoy, their star running back, to the Bills for linebacker Kiko Alonso. The people spoke under condition of anonymity because the teams had not announced the deal.
ESPN first reported the trade.
The deal has been agreed to, but can't be completed until the 2015 league season begins on Tuesday.
McCoy had an inconsistent season last year after leading the NFL with 1,607 yards rushing in 2013. At his best, McCoy is an elite multidimensional running back who has been a proven threat as both a runner and receiver.
He enjoyed his best season in 2013, scoring nine touchdowns rushing, adding 539 yards receiving and one touchdown.
One reason for McCoy's drop in production last season was a banged-up offensive line in which all five projected starters never played one game together.
McCoy's move to the Bills leaves C.J. Spiller in search of a new team. He is eligible to become a free agent next week.
Buffalo's 2010 first-round draft pick told the NFL Network the Bills informed him of the trade, and told him "they were going in that direction, pretty much giving me a 'Thank you for your service."'
Alonso will be reunited with Chip Kelly, who coached the linebacker at Oregon. Alonso made an immediate impact in Buffalo after being selected in the second round of the 2013 draft.
The Bucs confirmed the former Florida State star was in town Tuesday to sit down with club officials who will be involved in deciding whether to draft Winston. The team is also considering quarterback Marcus Mariota, the 2014 Heisman Trophy winner from Oregon.