He punched Ousmane Dabo, a former colleague at Manchester City, knocking him unconscious, and continued to hit him as he lay on the ground.

Team-mates who witnessed the assault were shocked by the violence.

Georgios Samaras said it was a scene "he would never forget". Paul Dickov attempted to stop the violence and received a punch.

Joey Barton, 25, pleaded guilty to assault occasioning actual bodily harm at Manchester Minshull Street Crown Court on Monday.

The Newcastle United midfielder was due to go on trial, but changed his plea to guilty after learning he was likely to receive a suspended sentence.

Outlining the events at Manchester City's training ground on May 1 last year, prosecutor Richard Vardon said it was an "explosive combination of football and violence".

The pair squared up to each other after a simmering row during a training match session, the court was told.

Barton shouted at Dabo: "You're f****** s****," Mr Vardon said.

Dabo, 31, was said to have felt intimidated that Barton had invaded his personal space as he shouted and swore at him.

The Frenchman pushed his shoulder with both hands, and in retaliation Barton punched him to the left side of his head, causing the Frenchman to fall to the ground and lose consciousness.

Mr Vardon said several witnesses said Barton continued to punch Dabo while he lay on top of the player, who was in a dazed state.

Mr Vardon said Mr Samaras was shocked by what he saw.

He said: "He had never seen such a violent incident happen on the football pitch in all his career and said he would never forget it."

Mr Vardon said Stuart Pearce, former City manager, saw Barton on top of Dabo hitting him.

He added that goalkeeper Joe Hart saw Barton punching Dabo "repeatedly in the face, about four or five times".

Dabo was treated in hospital for head trauma, an inflamed eye and bruised eyelids following the attack. He missed several games as a result of his injuries.

Mr Vardon said Barton has never apologised to Dabo - who was in court today - for the assault.

Barton is currently serving a six-month jail sentence for assault and affray following a punch up in a Liverpool fast-food restaurant on Boxing Day last year.

His football career has been marred by his actions off the pitch.

Manchester City fined him several times for bad behaviour, including stubbing a lit cigar into the eye of young team-mate Jamie Tandy during a club Christmas party, and for getting involved in a spat with an Everton supporter in Thailand.

Barton will be sentenced at Manchester Minshull Street Crown Court.