The Brazilian, who wore the shirt to his countryman's fancy-dress party, is adamant the stunt was a joke and was not meant to upset his side's supporters.
The 33-year-old, who arrived at Loftus Road from Inter last summer, was pictured wearing a full Chelsea kit while attending David Luiz's birthday party in London.
QPR has confirmed the matter will be dealt with internally, and the Brazilian goalkeeper has reiterated that the stunt was a joke and was not meant to upset his side's supporters.
“I would like to clarify that last night I attended David Luiz’s fancy dress birthday party and as a joke for my friend, my family and I dressed as him," Cesar said in a statement on QPR's official website.
“I want to assure everyone that absolutely no offense was intended."