Jorge Mendes is the frontrunner to sign Dele Alli to his agency Gestifute, Sky Sports News understands.
Alli is expected to switch agents when his contract runs out with Rob Segal and his company Impact Sports next year.
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The 21-year-old's current Tottenham contract runs until 2022 but initial talks have been held over another new deal that Spurs hope he will sign before he potentially switches to Mendes in 2018.
A number of top domestic football agencies, including Stellar, Base Soccer and Unique, have been interested in representing England regular Alli.
Alli's long-term close friend Harry Hickford, who also came through the ranks at MK Dons, and sports lawyer Ian Lynam are understood to be handling his negotiations.
Gestifute also represent Manchester United manager Jose Mourinho and a host of top players including Cristiano Ronaldo, Diego Costa and Manchester City players Nicolas Otamendi, Bernardo Silva and Ederson.
Alli has scored seven goals in 13 club appearances this season, including two in the 3-1 Champions League win over Real Madrid, ahead of Saturday's north London derby, live on Sky Sports.