Barton spent the 2012/13 campaign on loan at Marseille after being deemed surplus to requirements at Loftus Road.
The 30-year-old thoroughly enjoyed his time in France and had been hoping to complete a permanent switch this summer.
No deal has been put in place, though, as he remains tied to a long-term contract in England.
QPR boss Harry Redknapp admits he is in the dark when it comes to Barton's future, with there no indication that a compromise which suits all parties is close to being reached.
He told talkSPORT: "He wants to go to Marseille and he did very well there last year, but he's got two years left of his deal here.
"I think he's looking for the club to give him a payday here and then he'll go. I don't know how it's all going to end."
Barton missed the start of pre-season training at QPR, revealing that he was planning on working on his fitness by himself, but took to Twitter on Wednesday to confirm that he was heading back in.
He posted: "Up and off to training today. 1st day back. Like a new term at school. Albeit a school, you were once expelled from..."
Meanwhile, Redknapp has admitted that he is hoping to put the funds generated by the sale of Chris Samba back to Anzhi Makhachkala towards piecing together a promotion-winning squad.
He added: "Chris Samba did leave yesterday (Tuesday). We've got our money back and I thought it was a good deal for the club. It didn't really work out for him here.
"That gives us some ammunition though to go out and get four or five players with that money and improve the team as a whole."