Another day, another potential New England Patriots scandal. The Boston Globe has an article out detailing the questionable relationship between Tom Brady and a shady individual named Alejandro Guerrero, his "body coach" with whom he has a professional business relationship as well. I suggest you read the article by the Globe, as well as this summary by SBNation, but the short version is that Brady and Guerrero are business partners, and they have had a contractual relationship with the Patriots for several years. In other words, Brady receives a stream of revenue from the Patriots outside of his normal salary.
As of now, this is unlikely to turn into a full-scale scandal:
The NFL says it is aware of the arrangement and has taken no action, despite questions from some specialists in sports law and economics about whether teams should pay for services by for-profit companies owned by their active players and whether the relationship provides value to Brady that should be counted against the club’s salary cap.
The NFL doesn't seem to have an issue with this, as it fills a gray area in the Collective Bargaining Agreement. This is in contrast to the NBA, which prohibits teams from entering into agreements with player-owner businesses. That said, it's still borderline and sketchy, which as we all know, is standard operating procedure for the Patriots. Perhaps this partially explains why Brady was so willing to take less money in his last contract in what was widely considered to be a very team-friendly deal.