The controversial midfielder was appearing before a Football Association hearing this lunchtime over the violent conduct charge relating to the assault on Ousmane Dabo in training when Barton was a Manchester City player.

Barton has already appeared in court over the incident that took place in May 2007, and escaped with a suspended sentence while he was serving a six-month jail term for assaulting a teenager in Liverpool city centre.

Kevin Keegan had publicly backed the 26-year-old, saying that he was prepared to give the player a second chance, although that stance was believed to be at odds with Mike Ashley's view.

Keegan was due to appear at Barton's hearing as a character reference, but following his dramatic resignation as Newcastle manager last night it appears doubtful he will be in attendance.

Barton had been tipped to pick up anything from a 12-15-game ban for the incident, but former Newcastle manager Sam Allardyce – who signed Barton for £5.8m from City last year – has urged the FA to show clemency.

"It's going to do neither Joey Barton, Newcastle United nor football any good if they suspend him," Allardyce said.

"He has already paid his penalty. If you want to keep Joey Barton on the straight and narrow, it should be getting him playing football because that's where he is at the happiest in his life.

"To slap a severe punishment on him again would almost be as if they are doing it because it is politically correct and not because it is the right thing to do."