Horton and Fabregas were both on the pitch after the final whistle
The Football Association has written to Hull's managerial team over allegations that Arsenal's Cesc Fabregas spat at Tigers assistant manager Brian Horton.
BBC Sport understands the FA wants City manager Brown and Horton's accounts of events following Tuesday's stormy FA Cup quarter-final.
The match officials did not mention the alleged incident in their match report from the Emirates Stadium.
Spanish midfielder Fabregas has strenuously denied the allegation.
Brown claimed the incident with Fabregas, who did not play in the game due to injury but joined the Arsenal celebrations on the pitch after the final whistle, happened in the tunnel following the 2-1 defeat.
And Horton said on Wednesday: "I am speaking to the League Managers Association and want to take this further."
An LMA statement confirmed Horton had made contact, adding: "As the incidents fall firmly within the jurisdiction of the Football Association, who are making their investigations in the prescribed manner, neither the LMA nor Brian Horton will be making any further comment at this time."
Whichever way you want to look at it, he addressed that spitting incident at my assistant manager who has managed probably 1200 games in his career. Disgraceful act
Hull boss Phil Brown on Cesc Fabregas
The FA has written to Hull asking for their version of events after neither referee Mike Riley nor any of the other match officials mentioned anything of such an incident in their report.
Hull manager Brown told BBC Radio 5 Live: "Brian will receive the full support of the people of Hull, including my chairman.
"We'll go down the right channels and support Brian Horton."
The Football Association is awaiting the referee's report and any possible formal complaint from Hull's coaching staff.
Arsenal manager Arsene Wenger has said that he did not witness the incident, while Fabregas has denied the spitting allegations.
"I categorically deny that I spat at anybody after the match," said the Spanish international in a statement.
"I have never done this in my whole career on the pitch, so why would I do it when I am not even playing?
"I can understand the frustration of losing a game to a dubious goal, that has happened to me many times in my career as well, but this is not the fault of me or any of the Arsenal players."
Brown has questioned whether Fabregas should have been allowed on the pitch, adding that he thought his attire of jeans and a puffa jacket was unsuitable and that the Arsenal captain had behaved in an aggressive manner.
"The pictures in the national papers verify the aggression he was showing towards players and staff after the game. I could go on but I'm not one for crying over spilt milk," he added.
"I then witnessed him going down the tunnel and turning round and spitting at my assistant manager's feet.
"Whichever way you want to look at it, he addressed that spitting incident at my assistant manager who has managed probably 1200 games in his career. Disgraceful act."
Brown also revealed he was unhappy with an alleged lack of courtesy shown to him by Wenger in the clubs' two league meetings this season.
"It just shows how we've got up the noses of the Arsenal hierarchy.
"He wouldn't shake my hand when we beat them fairly 2-1 at the Emirates, he wouldn't shake my hand when they beat us, fairly, 3-1 at the KC Stadium."
However, photos and videos have since appeared on the internet contradicting Brown's claim that Wenger failed to shake hands after the match at the Emirates.
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