Barton is currently enjoying his loan spell at Marseille, but was quick to criticise his former team-mates following the Hoops' relegation on Sunday afternoon, describing some members of the squad as "maggots" shortly after the team's 0-0 draw at Reading.
The 30-year-old - who was banned for 12 matches and fined £75,000 by the Football Association for his behaviour in the defeat on the final day of last season at Manchester City - revealed it would be tough to leave the French club.
However, Fernandes insists unless a transfer fee can be agreed, then Barton, signed from Newcastle on a free in August 2011, would be expected back at pre-season training.
"Marseille have got to put an offer in. Joey is under contract and Joey would be a very useful player for Queens Park Rangers," Fernandes said on QPR Player.
"He helped Newcastle out (of the Championship). Some would say we lacked his fighting spirit in the midfield.
"But if Joey and Marseille want (the transfer), then we will talk.
"However, he is a QPR player, and is contracted to QPR.
"That has to be a financial deal which would have to be worked out if he wants to go to Marseille, but as far as I am concerned he is a QPR player and in the summer will come back."