Barton, 29, 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 review, QPR have imposed further sanctions on the controversial midfielder, and a club statement read: "QPR FC can confirm Joey Barton has been fined six weeks' wages and will no longer be club captain. If Barton seriously breaches the club's disciplinary procedures again, the club reserves the right to terminate his contract."
Barton, who is currently away on holiday, will not be part of Mark Hughes' squad for their pre-season tour of Asia in mid-July.
The former Hoops skipper, who earlier this month was arrested for affray following a night out in Liverpool with his girlfriend, issued an unreserved apology.
Barton said in a statement on the club's official website, "My behaviour was wrong and I accept the punishment that has been imposed upon me as a result. 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 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."
Source: PA
Source: PA