NFL: Rob Gronkowski returns from retirement, joins Tom Brady at Tampa Bay

NFL tight-end star Rob Gronkowski has come out of retirement and will reunite with former New England teammate Tom Brady, after a trade to the Tampa Bay Buccaneers.

According to ESPN, the Buccaneers will send a fourth-round pick to the Patriots, in return for a seventh-rounder and Gronkowski, who must pass a physical to complete the deal.

NFL Network reported Gronkowski, who turns 31 in May, has gained weight for a return to football, after sitting out the 2019 season.

'The Gronk' had one year and $US10 million remaining on his contract when he retired, so the Patriots still held his rights.

He has performed in WWE pro wrestling recently, winning the 24/7 title at Wrestlemania 36 earlier this month.

In a video published Monday, Gronkowski suggested he might team up with Brady in Tampa Bay, after the quarterback signed with the Buccaneers as a free agent in March.

"I'm feeling good right now, I'm happy where I'm at," Gronkowski said of retirement.

"You just never know, man. You never know, I'm not totally done."

In November, Gronkowski refused to say he was "never coming back", suggesting he could return to the league after a year or two away.

A five-time Pro Bowler and four-time first-team All-Pro, Gronkowski totalled 521 receptions for 7861 yards and 79 touchdowns across nine seasons for the Patriots from 2010-18. He and Brady combined for three Super Bowl victories during that span.

He had 47 catches for 682 yards and three scores in 13 games in 2018, battling a few nagging injuries.