Players from Middlesbrough and Manchester United reportedly had to be pulled apart after clashing in the tunnel following their Premier League meeting at the Riverside Stadium on Sunday afternoon.
Man United ran out 3-1 winners in the Premier League affair after goals from Marouane Fellaini, Jesse Lingard and Antonio Valencia secured all the points for the Red Devils.
Tempers flared in the latter stages of the match when Man United's Eric Bailly and Middlesbrough's Rudy Gestede clashed, while the home side's captain Ben Gibson also became involved in a scuffle.
According to The Mirror, there was also ill-feeling in the tunnel at the end of the match, and Bailly and Gestede had to be prised apart by security staff, while Gibson and Man United's Ashley Young were also said to be in the thick of the action.
Both clubs could now face disciplinary action from the Football Association depending on referee Jon Moss's take on proceedings at the end of the league fixture.