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."