Footballer Joey Barton has admitted assault after knocking out a team-mate in a training ground row.The Newcastle United midfielder pleaded guilty to one charge of assault occasioning actual bodily harm after attacking Frenchman Ousmane Dabo on May 1 last year, when both players were at Manchester City.Barton, 25, is already serving a six-month sentence for a drunken fight in a branch of McDonald's in Liverpool.Prosecutor Richard Vardon told Manchester Minshull Crown Court the pair squared up to each other in an "explosive combination of football and violence" during a training session.Dabo, 31, who now plays for Italian side Lazio, was said to have felt intimidated that Barton had invaded his personal space as he shouted and swore at him.The Frenchman pushed Barton's shoulder with both hands, and Barton retaliated by punching him to the left side of his head, knocking him out cold, the court heard.Mr Vardon added that several witnesses said Barton continued to punch Dabo while he lay dazed on the ground.Mr Vardon told the court one player, Georgios Samaras, said he had never seen such a violent incident on a training pitch in all his career.Barton had been due to stand trial over the incident but changed his plea shortly before the hearing after Judge Mushtaq Khokhar indicated he would impose a suspended sentence.The player, who has been capped once for England, will be sentenced on Tuesday morning.On May 20, Barton was jailed after admitting assault and affray following a fight in a McDonald's where he was filmed on CCTV repeatedly punching his victim in the face.Police later released graphic footage of the violent attack.