#4 Sign a world-class midfielder

Tottenham has multiple options in midfield. A world-class central midfielder would provide further depth and also cover for current inadequacies. Dembele, when fit, dominates midfield. However, his fitness often lets him down and his contract situation is also unclear. Dier lacks mobility and suffers from lapses of concentration.
Both Dembele and Dier are considered starters within the Tottenham midfield. Winks is young and has lots of potential but is not yet the finished article. Sissoko lacks technical ability, and that is not to say that these players are of average quality. They are all brilliant players but these flaws show the possibility for improvement. Sissoko is the only exception. I consider Sissoko an average player at best.
Despite that, he was forced to make a significant number of appearances for Tottenham last season due to injuries. Due to these reasons, there is a need for a world-class central midfielder, someone who would dictate play from deep and also contribute goals and assists on occasion.
Keita would have been an ideal signing had he not been purchased by Liverpool. Possible options which are available include Rabiot from PSG or Jorginho from Napoli.