FOXBOROUGH, Mass. -- The San Francisco 49ers are now willing to listen to trade offers for Brandon Aiyuk and have given the star wide receiver permission to negotiate a contract with other teams, sources told ESPN.

It represents a significant change for the 49ers, who did not have the same willingness to listen to trade offers at the start of training camp, sources said.

The New England Patriots and Cleveland Browns both have been in contact with the Niners and are interested in trading for Aiyuk, sources told ESPN. The Pittsburgh Steelers also were interested but do not appear to be a potential trade destination any longer, according to sources.

The Patriots have been attempting to acquire Aiyuk for months, and it has been a slow process from their side, according to sources.

Patriots first-year head coach Jerod Mayo wouldn't confirm that the Patriots have been granted permission to negotiate with Aiyuk, but did acknowledge that he spoke with current New England receiver Kendrick Bourne, because Bourne's name has surfaced in reports as someone who could be included in a potential trade.

"It was a good conversation. Once again, I feel like the story is so much further along than anything else," Mayo said Tuesday before the Patriots' practice. "I just wanted to make sure we cleared the air. I do believe in being transparent with the players and really setting those guys at ease."

It's still a fluid situation that could lead to several outcomes, including Aiyuk staying with the 49ers and playing out the fifth-year option on his rookie deal that would pay him $14.124 million, sources said. Other teams are willing to pay Aiyuk more than twice as much, but he has balked so far at multiple offers, according to sources.

The 49ers also have to be comfortable with any trade compensation, and sources told ESPN that the reigning NFC champions are willing to keep Aiyuk.

NBC Sports Bay Area reported late Monday night that the 49ers have "negotiated the framework of trades" that would send Aiyuk to the Patriots or Browns.

Aiyuk, 26, reported for the 49ers' training camp but has not practiced as he seeks a new deal.

The Patriots' lengthy pursuit of Aiyuk traces back to February, when executive vice president of player personnel Eliot Wolf shared his hope to "weaponize the offense." The Patriots selected Drake Maye with the No. 3 overall pick in the draft, and one of their goals has been to surround the former North Carolina quarterback with more talent to aid in his development.

New England attempted in March to sign free agent wide receiver Calvin Ridley, who ultimately landed with the Tennessee Titans on a four-year, $92 million deal.