Southampton are reportedly considering whether to take legal action against Atletico Madrid in their attempts to sign Toby Alderweireld on a permanent basis.
The Saints are believed to have secured a €6.8m buy-out option when they signed the Belgian defender on loan last summer, but this has not stopped Atleti from negotiating a sale with fellow Premier League club Tottenham Hotspur.
Los Colchoneros also had the option of revoking the clause by paying Southampton a €1.5m fee, but Sky Sports claims they did not do so in time.
Consequently, Southampton are now threatening Atleti with legal proceedings if they do not honour their part of the agreement.
The 26-year-old is understood to be happy with a switch to either club but has not yet commented on his future.