Reports suggest that the one-time England international is a key defensive target for manager Ronald Koeman, who is looking to plug holes in a unit that has been weakened by the departure of Toby Alderweireld and injury to Florin Gardos.
The Dutchman is said to be keen to secure a temporary move with a view to an £8million permanent deal for Caulker. However, the Saints will have to battle with West Bromwich Albion, who are also interested in securing the 23-year-old's signature - say the Daily Mail.
Caulker made 35 appearances throughout QPR's previous top flight campaign, but he could do little to prevent the club's return to the Championship.
He found success in 54% of his total duels, winning 142 of his 249 aerial battles and 30 of his 68 attempted tackles. Meanwhile, he averaged 13 defensive actions per appearance - a superior rate to any of his team-mates.
Despite his efforts, Caulker's time at Rangers will remain a blemish on his career. The 23-year-old experienced what can only be described as a nightmare season following his move from Cardiff City, with whom he also experienced relegation the year before.
Operating under Ronald Koeman at Southampton, the Englishman would be expected to see himself improve as a player. He remains a fantastic prospect, but he needs stability as well as the right manager in order to help him realise his potential.
An initial loan deal makes perfect sense for both parties in this case. A temporary move to St. Mary's removes the 23-year-old from the Loftus Road wage bill for at least a season, while the Saints have just under a year to assess his suitability for the club.
Should he impress for the south coast outfit, an £8million purchase fee will surely be considered a steal.