The Cameroon international moved to Loftus Road last summer, with Joey Barton making a loan move to Marseille as part of the deal.
But, after being unable to help QPR avoid relegation from the Barclays Premier League, there was a message sent to Barton from Mbia's Twitter account asking him if he was interested in returning to the west London club in his place.
It read: "@Joey7Barton: Do you want to rechange (sic) your seat with me?"
The club acknowledged the message and revealed Mbia informed them he was not responsible for them. However, Rangers have now fined the midfielder.
QPR spokesperson Ian Taylor wrote on Twitter: "The club has concluded its investigation following a series of Tweets which appeared on Stephane Mbia's official Twitter account.
"Stephane has stressed to the club that he is not responsible for the Tweets.
"However the club is of the view that every player that has a Twitter account is ultimately responsible for what appears on it.
"As a result, Stephane has been fined and warned in relation to his future conduct. The club will be making no further comment."
- Sports & Recreation
- Joey Barton