Caulker, 23, came up through the ranks at Tottenham, and despite being touted for a bright future at White Hart Lane, he was sold to Cardiff City back in 2013.
The centre back suffered immediate relegation with the Bluebirds in 2014, and moved on to QPR - only to once again suffer relegation back to the Championship.
This term, Caulker has been farmed out on loan to Southampton, but it isn't going much better for the defender on the South Coast either.
Caulker has struggled to make an impact for Ronald Koeman's side, and has often looked shaky in defence when he has played - prompting suggestions that he could actually go back to QPR in January, especially given that Southampton landed Virgil van Dijk from Celtic back in September.
Now, The Sun report that Sunderland are interested in a £5m deal for Caulker, but any move for the defender could be complicated.
QPR are allegedly unwilling to take Caulker back to Loftus Road unless they know a team will buy him almost immediately, as they can't afford to shoulder the burden of his wages.
There would ultimately need to be agreements between Southampton, QPR and Sunderland to make any deal possible, but if all parties are willing to sanction the deal, Caulker could end up playing in a different team's red and white stripes this season.