Because a player can't be traded unless he is under contract, Butler's status was in limbo until he signed the $3.91 million tender.
Butler had not signed the tender in hopes that another NFL team might sign him to an offer sheet before Friday's deadline. He visited one team, the New Orleans Saints, earlier in free agency.
The Saints didn't plan to sign Butler to an offer sheet, but at the NFL's annual meeting in March, coach Sean Payton seemed to hint the club could be interested in a different scenario.
"It's ongoing, if you will," Payton said at the time, pointing out that the Saints and Patriots couldn't have trade talks about Butler unless he was under contract. "For us, it was a chance to meet him, put him on the board, find out how much football he knows. I think it was a good step."
The Saints have made it an offseason priority to improve their defense. The Patriots, meanwhile, signed cornerback Stephon Gilmore to a top-of-the-market five-year, $65 million contract as an unrestricted free agent and could be enticed to recoup some draft capital in a trade involving Butler, who will be an unrestricted free agent after the 2017 season.
The Patriots don't have a 2017 draft pick until early in the third round (No. 72 overall).
Another scenario is holding on to Butler for this season and pairing him with Gilmore in what would be one of the NFL's better one-two combinations.
ESPN NFL Insider Field Yates first reported news of Butler signing his tender.