The fee, believed to be in the region of £35M, would be a club-record transfer, with just a medical and work permit left to configure after personal terms were agreed between Spurs and the centre-back.
The highly rated 21-year-old comes from Holland with a stacked reputation, as his defensive performances helped Ajax reach the Europa League final last season.
Sanchez to start?
It's though that once the transfer goes through, he'll be making a strong push for a starting spot in Mauricio Pochettino's side, likely alongside Toby Alderweireld and Jan Vertonghen when the Argentine field's a back three formation.
When, or if, the Spurs boss reverts to a 4-2-3-1, Sanchez is expected to be third choice in the pecking order for now.
The transfer could set about a catalyst of moves in terms of defenders, with Kevin Wimmer being targeted by Southampton, something that could therefore lead to a knock on effect of Virgil Van Dijk's departure.
Tottenham fans will only be interested in the Sanchez signing though, as they finally add to a squad that came second in the Premier League last season, following a frustrating summer that hadn't seen any incoming's up to this point.
Things reached boiling point in recent weeks as left-back Danny Rose gave a revealing interview, criticising Spurs' buying policy and suggesting that he understood why fellow full-back Kyle Walker had been keen on a switch to Manchester City earlier this summer.
The Sanchez signing will appease fans for now, but it's thought that more moves are wanted by Pochettino before the window closes in around two weeks.