The Londoners have been linked with the player for a while now and it appears that Daniel Levy is a fan of the defender as per Het Nieuwsblad (via HITC).
Castagne would be a sensible signing for Tottenham this summer and it will be interesting to see if the Premier League side can convince the Italians to sell.
Mourinho needs more depth in his full-back positions and the Belgian could push Serge Aurier for the starting berth. The competition for places will bring out the best in both players and it will help Spurs improve.