The FA is investigating an altercation between Crawley Town defender Paul Connolly and a Brentford supporter during their League One clash at Griffin Park on Tuesday.
Sky Sports footage shows Connolly, 30, confronting a man in the lower tier of the Braemar Road stand and appearing to swing an arm towards him after the ball was thrown towards the player from the crowd.
Brentford, who won the game 1-0 thanks to a 58th-minute header from midfielder Jonathan Douglas, have said they will assist any investigation into the incident and will also consult with police, the Football League and referee Stephen Martin before making further comment.
Chief executive Mark Devlin said: "It does look as though the ball went into the crowd, and from what I could see it was thrown towards the player.
"The player didn't like it and there appeared to be an exchange, whether it was a slap or a punch or whatever.
"The referee has moved in and a plastic bottle has come onto the pitch, so no doubt we'll hear from the Football League about that one as well.
"The club will wait to see what the police say and then take it up with Crawley. If the Football League asks us for our input we will investigate it and let them know from our point of view what's gone on."
Brentford's victory moved them nine points clear in the automatic promotion places after third-placed Rotherham lost at Sheffield United.
Mark Warburton's side now have five games to go to reach the second tier of English football for the first time since 1992.