Toby Alderweireld's decision to join Tottenham and a serious knee injury sustained by Florin Gardos has heightened the need to bring in defensive reinforcements at St Mary's.
Saints manager Ronald Koeman has spoken of his wish to acquire at least one more centre-back, as well as add some extra height in defence - a role it appears Caulker will now help fill.
Signed by QPR last summer, Press Association Sport understands the 23-year-old is again on the move with a loan deal at St Mary's close to completion.
Reports suggest Caulker will move with a view to an Â£8million permanent transfer - the amount QPR paid to bring him in from Cardiff last year.
The centre-back will be looking to avoid a third straight relegation from the Premier League at Saints and to add to his sole England cap won three years ago.
Source : PA