MAURICIO Pochettino must pay around £2m to Saints if he wants to join Tottenham with a year left on his existing St Mary's contract.
Former chairman Nicola Cortese inserted such a clause in the manager's contract should he wish to leave early with his contract due to end in the summer of 2015.
Pochettino and Ajax coach Frank De Boer are the front-runners to replace Tim Sherwood, who was sacked yesterday as Tottenham boss after less than six months in the job.
Sherwood left with a 59 per cent Premier League win record, compared to Pochettino's 41 per cent during the same time frame.
Overall, during his 54 league games in charge of Saints, Pochettino's win record is 35 per cent.
De Boer has just won his fourth successive Dutch League title with Ajax, and in his three full seasons in charge has only lost eight games in total.
As a result, he has Champions League managerial experience.
Tottenham have qualified for next season's Europa League after finishing sixth.
Pochettino has never managed in European club competitions and earlier this year stated his dislike of the Europa League.