Joey Barton faces one of the lengthiest suspensions in English football history after being charged with violent conduct by the Football Association. While it emerged last night that the midfield player has effectively been slapped on the wrist by Newcastle United after his release from Manchester Prison on Monday, he could yet be banned for 15 matches.

Newcastle have, for legal reasons, been unable to cut Barton’s £65,000-a-week wages despite the desire of Mike Ashley, the owner, to impose strict disciplinary sanctions on the England international after his conviction for assault and affray in Liverpool city centre on December 27. They had, however, already imposed a club fine and did not pay him during his 74 days of incarceration.

Having reconciled themselves to reintroducing Barton into Kevin Keegan’s squad – the manager said yesterday that the player would “not take much getting fit” after his spell of inactivity – Newcastle officials were stunned by the FA’s action, which relates to Barton’s training-ground assault last year on Ousmane Dabo, his former Manchester City teammate.

In a statement, the club revealed that they had “sought clarification from the Football Association as to why the decision has been reached now, given the incident occurred nearly 15 months ago”. In response, FA sources insisted that clarification had already been given; they were duty-bound to await the conclusion of any legal case before launching their own investigation.

The Times can reveal that Barton has been stripped of other perks at Newcastle, such as a corporate box at St James’ Park and the occasional use of a club driver, but the English game’s governing body insists that football must have a role in policing itself. The 25-year-old was recently given a four-month sentence, suspended for two years, ordered to pay £3,000 compensation and to perform 200 hours of community service as a result of the Dabo incident.

Newcastle said that Barton will request a personal hearing into the charge – he has until August 13 to respond – but, having already admitted in court to assaulting Dabo, the FA does not expect him to contest it. The FA has applied to the courts for the relevant certificate of conviction, which details the circumstances behind the case and the evidence given.

While there is no direct precedent for such a matter, the FA has previously acted over training-ground skirmishes, banning John Hartson for three matches and fining him £20,000 when Eyal Berkovic, then his teammate at West Ham United, was kicked in the head in an episode caught on camera.

While the final punishment will be determined by an independent panel, the FA argues that Barton’s indiscretion was at least of equal severity to that of Ben Thatcher in August 2006 when the former Manchester City defender knocked out Pedro Mendes with his forearm in the Premier League match at home to Portsmouth; Thatcher was banned for eight games, with 15 suspended for two years.

The latest development will be a sharp blow to Newcastle and Keegan, in particular. The manager spoke passionately last weekend in defence of Barton’s right to rehabilitation after a summer during which the club had explored the possibility of dismissal. Newcastle failed to persuade Barton to agree a new £30,000-a-week contract, which included a clause enabling him to join any interested club for £3 million.

Before the FA’s announcement, Keegan, whose side play Hertha Berlin in Majorca tonight, had insisted that Barton, who is training on Tyneside, would not be rushed into action.