Cesar, 33, joined QPR from Inter Milan last summer but has been unable to prevent Harry Redknapp's side from slipping to the edge of Barclays Premier League relegation.
He was an unused substitute as fellow strugglers Stoke picked up a crucial victory at Loftus Road on Saturday, a result that means Rangers could return to the npower Championship by Sunday afternoon.
Cesar was pictured wearing the home shirt of QPR's London rivals Chelsea as he posed with countryman David Luiz at a birthday party for the Blues defender.
The image was quickly circulated on social media platforms, with QPR head of communications Ian Taylor writing later on Twitter: "The club is aware of an image of Julio Cesar circulating on social networking feeds.
"The image, which appeared on an Instagram account, has since been deleted. The club will be dealing with this issue internally."
Source: PA
Source: PA