Joey Barton admitted he was "reckless and stupid" after being stripped of the QPR captaincy and fined six weeks wages for his sending off against Manchester City on the final day of the Barclays Premier League season.
The 29-year-old was hit with a 12-match ban and fined £75,000 by a Football Association-appointed independent regulatory commission last month after being dismissed for elbowing Carlos Tevez, then kicking out at Sergio Aguero as he left the pitch in the match on May 13 before aiming a headbutt in the direction of Vincent Kompany.
Following their own internal investigation, QPR have now imposed further sanctions on the controversial midfielder, signed last summer on a lucrative four-year deal following a free transfer from Newcastle, and warned Barton his contract will be terminated for any further transgressions.
Barton, who is currently away on holiday, apologised in a statement on the club's official website, which he later expanded on in a series of Twitter posts.
He said: "I was reckless and deserved every punishment I received.
"Money comes and goes, it's not important to me. Losing the captaincy and missing 12 games is what really hurts.
"I was stupid and that what happens when u [sic] do dumb things. I am confident ill [sic] bounce back. Cannot wait.
"That's all I have to say on the matter. I wish to put it behind me now and help QPR, once available of course, push on towards the top half.
"Have a good day people. Thanks for all the lovely tweets of support. Speak soon xx."
Barton has a long history of controversy, both on and off the pitch.
In 2008, he was given a six-month jail term after admitting assault and affray. During his time as a player at Manchester City, Barton was fined after he stubbed a lit cigar in the eye of young team-mate Jamie Tandy during the club's Christmas party.
Earlier this month, Barton was arrested for affray following a night out in Liverpool with his girlfriend.
In his official club statement, the player issued an unreserved apology.
"My behaviour was wrong and I accept the punishment that has been imposed upon me as a result," the statement read.
"I apologise to the manager, my team-mates and of course the QPR fans for my actions.
"I also apologise to the Manchester City players, staff and supporters."
QPR also confirmed Barton will not be part of the squad which heads to Asia for a pre-season tour in mid-July.
Chief executive Philip Beard defended the club's punishment and is hopeful the player will be able to put the incident behind him as they prepare for a second season back in the Premier League.
He said: "It was important that we took our time to make sure we came to the correct decision, which I believe we have achieved.
"Joey's behaviour, which led to his red card at Manchester City, and his subsequent actions were completely unacceptable and we have made our feelings on this matter known to him.
"I am really pleased with the way in which the club and Joey have worked towards reaching a sensible conclusion and we fully believe he will respond to these sanctions in the correct manner."
Joey Barton factfile:
1982: Born Huyton, Merseyside, September 2.
2003: April - Makes Manchester City debut in a 2-0 defeat at Bolton.
2004: February - Sent off at half-time in an FA Cup tie at Tottenham with his team 3-0 down. City go on to win 4-3.
April - Storms out of Eastlands before kick-off after being dropped from the side to face Southampton.
July - Criticised by manager Kevin Keegan for causing a mass brawl in a pre-season friendly at Doncaster.
December - Stubs lit cigar in the eye of young team-mate Jamie Tandy during City's Christmas party. Fined six weeks' wages by the club. Forced to pay four weeks' salary - approximately £60,000 - immediately, with a further two weeks suspended for a year. Tandy later sued Barton, winning £65,000 in damages.
2005: May - Barton breaks leg of 35-year-old pedestrian while driving his car at 2am in Liverpool city centre.
July 22 - Involved in an altercation with a 15-year-old Everton fan at City's team hotel in Bangkok, where the team are playing in the FA Premier League Trophy.
July 27 - Fined eight weeks' wages by City after being found guilty of gross misconduct in the Bangkok incident. Agrees to undertake a programme of rehabilitation.
2006: January 30 - Hands in a transfer request, which is rejected.
September 30 - Drops his shorts in direction of Everton fans following City's 1-1 draw at Goodison Park. Later charged by the Football Association over the incident and fined £2,000.
2007: February 7 - Makes senior England debut as a 78th-minute substitute against Spain.
May 1 - Suspended by City for the rest of the season after training-ground altercation with Ousmane Dabo.
June 14 - Completes £5.8million move to Newcastle.
August 2 - Charged with assault over Dabo incident.
October 4 - Appears in court charged with Dabo assault. Indicates he will plead not guilty.
October 22 - Makes Newcastle debut in 3-1 victory over Tottenham.
December 1 - Causes controversy by describing the St James' Park crowd as "vicious".
December 28 - Charged with common assault and affray and refused bail after being arrested in Liverpool city centre the previous day.
2008: January 3 - Released from custody after being granted bail.
May 20 - Admits assault and affray and is jailed for six months at Liverpool Crown Court.
July 1 - Receives four-month suspended sentence for assaulting Dabo.
July 28 - Released from prison.
July 31 - The FA charge Barton with violent conduct over the Dabo incident.
August 30 - Returns as a substitute for Newcastle away to Arsenal.
September 5 - Banned by the FA for 12 matches - six of which are suspended - and fined £25,000 after admitting violent conduct charge in relation to Dabo incident.
2009: May 3 - Sent off against Liverpool for late challenge on Xabi Alonso.
May 5 - Suspended until further notice by Newcastle.
November 11 - Charged with violent conduct by FA after allegedly punching Blackburn's Morten Gamst Pedersen during a league match.
2011: August 1 - Newcastle transfer-list Barton after a series of Twitter comments criticising the club, making him available on a free transfer.
August 26 - Signs for QPR on a four-year deal and is made club captain.
September 17 - Scores first QPR goal, but is also involved in a confrontation with Karl Henry, whom he later criticises on Twitter.
2012: January 2 - Receives first red card for Rangers for butting Norwich's Bradley Johnson.
March 21 - Booed by QPR fans after a poor performance against Liverpool. Criticises his treatment on Twitter.
May 13 - Dismissed for striking Manchester City's Carlos Tevez on final day of season. He goes on to knee Sergio Aguero from behind, thrust his head toward Vincent Kompany and is restrained when attempting to confront Mario Balotelli before walking off the pitch.
May 14 - Charged with two acts of violent conduct by the Football Association following his actions against Manchester City.
May 16 - QPR announce an investigation into Barton's conduct in the game against City.
May 23 - FA announce an independent regulatory commission found Barton guilty of both violent conduct charges, resulting in a ban of 12 games and a fine of £75,000.
June 5 - Punched in the face after being involved in an altercation with two men outside a nightclub in Liverpool city centre.
June 25 - Fined six weeks wages and stripped of the club captaincy by QPR following an internal investigation into events in the match against Manchester City.