This statement can be traced back to a website, 'America's Last Line of Defense' which describes its output as satirical or mainly humorous in nature.
The Snopes article claims that on June 29th, America's Last Line of Defense (ALLOD), a satirical news website that focuses on parody, posted an article titled "Tom Brady: 'If Anyone on My Team Kneels, I Quit.'" The Snopes asserts that this is not a factual recounting of real-life events and that everything on the ALLOD website is fiction. Furthermore, according to an ABC article from June 2018, Tom Brady has expressed his respect towards players who choose to kneel during the National Anthem. The ABC article states that Tom Brady felt the kneeling protests had prompted many healthy conversations around racial injustice in America.