The Newcastle midfielder was belatedly charged with violent conduct by the Football Association on Thursday afternoon over his training ground assault on Ousmane Dabo 15 months ago.
Barton, 25, was given a four-month prison sentence, suspended for two years, on July 1 after admitting assault occasioning actual bodily harm on his former Manchester City team-mate in May last year.
The FA were unable to launch their own investigation into the incident - of which there is no video footage - until the completion of the criminal investigation and court case.
FA: "Newcastle United can confirm that it has received documentation from the Football Association stating that it is charging Joey Barton with misconduct in relation to the incident that occurred with Ousmane Dabo in May 2007, at a time when he was a registered player of Manchester City," a club statement read
"The club has sought clarification from the Football Association as to why this decision has been reached now, given the incident occurred nearly 15 months ago.
"Joey will be requesting a personal hearing in relation to the charge and the club will be making no further comment on the matter at this time."
Barton now has until August 13 to respond to the charge.
There is no maximum sentence which could be issued to Barton by the FA and, given the severity of the attack on Dabo, a lengthy ban and possible fine would be the likely outcome were he found culpable.
It is understood that the FA will strongly contest any claim by Barton that further punishment for the offence would be a case of 'double jeopardy', given that an employee in any industry would expect to suffer professionally for a criminal offence committed at work.
When Eyal Berkovic was kicked in the head by West Ham team-mate John Hartson during a training session in October 1998, he was fined £20,000 and banned for three matches the following February, although the FA admit there is no direct precedent for such a severe, non-match attack.
When then Manchester City defender Ben Thatcher knocked out Portsmouth's Pedro Mendes with a forearm smash during a game two years ago he was banned for eight games, with a further 15 suspended for two years.
Trouble has followed Barton throughout his career with previous misdemeanours ... mainly against KIDS!
They include a fight with a 15-year-old fan during a pre-season trip to Bangkok in 2005 and an incident at a Christmas party in 2004 when he stubbed a cigar out in the eye of City youngster Jamie Tandy. And at Christmas when he attacked a 16-year old in Liverpool ... knocking out his front teeth ... and the kid had done no more than go to McDonalds for a meal.