An allegation of racial abuse during Saturday's match between Middlesbrough and Blackburn is being investigated by the Football Association.
Rovers striker Rudy Gestede appeared to react angrily to a gesture from the crowd at the end of the 1-1 draw.
The FA has contacted both clubs after referee Mark Clattenburg mentioned the incident in his report, while the police have also been notified.
Gestede equalised as Boro claimed a foul on keeper Dimi Konstantopoulos.
The goal, in the fifth minute of stoppage time, denied the home side a victory that would have moved them into the Championship's top two.
Following the final whistle, Benin international Gestede looked upset by an incident allegedly involving a section of the home support and was pictured appearing to mimic a gesture to his Blackburn team-mates.
Confirmation of the FA investigation has come a day after it charged Middlesbrough boss Aitor Karanka with improper conduct.
Karanka was sent to the stands by Clattenburg in the aftermath of Gestede's goal.
In his post-match press conference, the Boro boss said Clattenburg sent him from the dugout for pushing the fourth official David Coote.
But Karanka denied doing anything wrong, saying after the game: "I read that I pushed the fourth official or did a lot of things that are not true; I argued with the fourth official. I don't know if I have to speak to somebody to explain my behaviour."