Harry Redknapp’s side have already recruited Rio Ferdinand on a one-year deal following the expiry of the centre-back’s contract with Manchester United and are hoping to pair him up with Caulker at the back.

The R's will depart on a pre-season tour to Germany on Monday but they remain keen to close a deal for the 22-year-old Londoner in time for him to join them later on the tour.

Caulker’s contract with Cardiff contains a relegation release clause, meaning he is free to leave the club for a fee thought to be in the region of £8million.

QPR have met that price along with Southampton, whose Croatia defender Dejan Lovren is still wanted by Liverpool.