Toby Alderweireld has admitted that he is 'unsure' of his long-term future in the game.
"There is provision that Atletico can take [me] back if [they] want to," he told reporters.
"For me, next year the construction is complicated. I understand. We will sit down together after this season with all the parties and see what is the best solution.
"I will get the chance to show [my talents at Southampton] but, if I have two weeks in a row when I do not perform well, I will move to the bench."
Alderweireld, 25, could make his Saints debut against Newcastle United on Sunday.