Mike Florio of Pro Football Talk reported the news Sunday, citing "a source with knowledge of the situation."
This comes after Adam Schefter of ESPN reported Wednesday that Brady hadn't fully committed to suiting up for the Patriots during the upcoming campaign "even though people who know him believe he will be back."
Schefter also reported Gronkowski hadn't made an official decision on whether he would play.
According to Florio, Brady and Gronkowski are among the Patriots who "continue to be salty" regarding head coach Bill Belichick's decision to bench cornerback Malcolm Butler during the Super Bowl loss to the Philadelphia Eagles. Butler since signed with the Tennessee Titans and likely would have provided a much-needed boost for a New England defense that struggled with Philadelphia's attack.
Off-field concerns regarding the Patriots have been in the spotlight since Seth Wickersham of ESPN.com reported on power struggles between Brady, Belichick and owner Robert Kraft in January. Among the issues were Belichick's preference not to trade quarterback Jimmy Garoppolo and his difference of opinion with Brady on the quarterback's body coach and business partner, Alex Guerrero.
Even with the off-field headlines and Brady and Gronkowski's delay in fully committing to a return, the Patriots figure to be on the short list of Super Bowl contenders if they do both play.
They have made three of the last four Super Bowls, winning two of them, and have nine straight AFC East titles. The Brady and Gronkowski combination is a primary reason for the success as two of the best players in NFL history at their respective positions.
Gronkowski will likely be even more important than usual in 2018 after New England lost wide receiver Danny Amendola (Miami Dolphins) and running back Dion Lewis (Tennessee Titans) to free agency and traded receiver Brandin Cooks. What's more, wide receiver Julian Edelman is returning from a torn ACL.