The Gunners were asked by the Football Association to provide their observations, and according to manager Arsene Wenger, they have now decided to take the matter further.

Fabregas, who was not playing against Hull because of a knee injury, issued a statement on the evening of the incident to deny he spat at Horton in the tunnel.

Wenger feels there is no case to answer.

"Fabregas has been charged for improper conduct on the night," the Arsenal manager said, speaking at today's press conference ahead of the Barclays Premier League game against Middlesbrough on Sunday.

"I always said we are always very open to co-operate with any investigation.

"I personally looked at the reports, at the video evidence and there is nothing in there against Cesc."

Should the charges be proven, Fabregas - who missed more than three months of the campaign with a knee problem which required surgery - could face a suspension.

However, that would only be for domestic matches and as such would not cover the forthcoming Champions League semi-final against Manchester United.

Wenger continued: "I dont know if we will appeal - I will see what we can do about that.

"At the start, I am not a great fan of appealing because I said we are very open to co-operate and now I dont think we should stop that.

"I am very positive that there was enough evidence in what I have seen that the case should have been dropped."

Hull manager Phil Brown brought the alleged incident to light immediately after his side's defeat, but has also been charged by the FA following his outburst at referee Mike Riley.

A statement from the FA read: "Cesc Fabregas and Phil Brown have both been charged with improper conduct.

"The charges relate to matters arising from the FA Cup match between Arsenal and Hull at the Emirates Stadium on 17 March.

"Fabregas faces two charges of improper conduct relating to his conduct on the pitch following the game.

"One charge concerns his behaviour in coming onto the pitch after the final whistle, the second charge relates to an alleged spitting incident.

"The charges are based on submissions from Hull City and video evidence.

"Brown is charged with improper conduct and/or bringing the game into disrepute in relation to media comments made after the game concerning referee Mike Riley.

"Fabregas and Brown have until 12 May to respond."

Should Fabregas be found guilty and handed a suspension, in theory his Premier League season would be over.

Arsenal, who are out of the FA Cup, face what could be a crucial clash in the title race when they head to Old Trafford on May 16 before ending the domestic campaign against Stoke the following Sunday.

However, any ban could also be carried over into next season.

Neither referee Riley nor any of the other match officials mentioned anything of such an incident in their report to Soho Square.

Horton, though, had contacted the League Managers Association to lodge a complaint before Hull were asked by the FA to submit their observations.

Fabregas refuted all of the allegations.

He said: "I was on the pitch at the end of the game celebrating with my team-mates, but I promise I did not do anything wrong."

Back on the pitch, Arsenal return to action against Middlesbrough following their midweek trip to Liverpool which ended in an amazing 4-4 draw.

Wenger could see his defensive options boosted by the return of goalkeeper Manuel Almunia and Johan Djourou from injury, while Togo striker Emmanuel Adebayor is expected to have shaken off his hamstring problem.

However, leading scorer Robin van Persie continues to be troubled by a groin problem and will not feature either against Boro or United next week.

Wenger accepts his overworked rearguard have been "fatigued" by their recent efforts, but agreed split-second decisions must improve.

"The game is made of good and bad decisions and it is sometimes good just to clear the ball," said the Arsenal manager, who watched his side throw away a 4-3 lead after going ahead in stoppage-time at Anfield.

"However, I still believe the basic rule is to be constructive out from the back and that is what we try to do.

"But of course when sometimes you have to kick the ball into the stand to keep the result, I encourage the players to do it. It has to be the best decision of the time."

Boro have been something of a bogey side for Arsenal since Gareth Southgate took over, with four 1-1 draws and one defeat in the five encounters from September 2006.

Wenger is expecting another tough encounter against the relegation battlers on Sunday.

"They are always difficult," he said. "They are a good young side who made a bad start in the season, but I believe they are a good team.

"They have a good young promising manager and the future will show that."

Hull this afternoon issued a statement from chairman Paul Duffen, backing his staff over their claims.

"I have always welcomed the Football Association's investigation into events at the Emirates Stadium following the final whistle of our FA Cup quarter-final.

"It is no surprise to me that the FA have decided to bring the charges that they have announced this afternoon as I have always been confident in Phil Brown's and Brian Horton's accounts of events on that day.

"I will not comment further at this time as this matter is the subject of a disciplinary charge, but I have always known that Phil and Brian tell the truth."