Brown took part in his first practice with the Patriots on Wednesday, a day after his former trainer filed a civil lawsuit in the Southern District of Florida accusing him of sexual assault in three separate incidents.
"On Antonio's situation, both Antonio and his representatives have made statements and so I'm not going to be expanding on any of those," Belichick told reporters. "They are what they are. We've looked into the situation. We're taking it very seriously all the way through the organization. I'm sure there are questions, but I'm not going to be entering any discussion about that."
After the statement, Belichick declined to answer additional questions, including the wideout's status for Sunday's game against the Miami Dolphins. The longtime Patriots coach repeatedly said, "We're working on Miami."
League sources told NFL Media that the NFL's investigation into the allegations against Brown will be handled as quickly as possible.
The league could place Brown on the commissioner's exempt list while the investigation takes place. A player on the commissioner's exempt list can't practice or attend games, but is allowed at the team's facility for meetings, medical treatment, workouts and other permitted non-football activities if allowed by the team.
The lawsuit was filed Tuesday, a day after Brown officially signed with the Patriots. Brown's lawyer, Darren Heitner, said the pass-catcher denies the allegations and plans to pursue multiple legal options.
"Mr. Brown denies each and every allegation in the lawsuit," Heitner said in a statement. "He will pursue all legal remedies to not only clear his name but to also protect other professional athletes against false accusations."
The Pittsburgh Steelers originally traded Brown to the Oakland Raiders in the off-season. After suffering frostbite on both of his feet, fights with the league over his helmet and multiple fines, the Raiders eventually released the wide receiver.
Brown signed with the Patriots hours after the Raiders granted his release.