The 29-year-old received a straight red card for violent conduct after clashing with Argentina striker Carlos Tévez during QPR’s 3-2 defeat at the Etihad Stadium on the final day of the season.
The midfielder also lashed out at Sergio Aguero and Vincent Kompany before being escorted off the pitch by former City team-mate Micah Richards and QPR staff.
Barton was handed a four-game ban for the original offence with Tévez and received a further eight-game suspension for the incident with Aguero and Kompany.
QPR confirmed that Barton will not be appealing against the ruling, and the club will now undertake their own investigation into the events at the Etihad.
A statement from the London outfit on Friday read: “Queens Park Rangers Football Club can confirm it has now started a full internal investigation in relation to Joey Barton’s dismissal and subsequent events against Manchester City on the final day of the 2012-13 Barclays Premier League season.
“The QPR midfielder will not appeal against the independent Regulatory Commission’s decision made on Wednesday and he and his team are now working in full cooperation with the club to assist in the internal investigation.
“The club expects the investigation to last at least two weeks. During this period, no one from the club or Joey Barton himself will make any further comment.”
Barton received two red cards this season, with the former Newcastle United midfielder dismissed for head-butting Norwich City’s Bradley Johnson during a 2-1 defeat at Loftus Road in January.
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