I think it is easy to get carried away that Kulu is gone and see the 40m but I don't think it is that great a deal.
I think it will most likely be that Spurs don't get top 4 and don't take the option on him. We then get back a player who has flopped at 2 clubs and have a more difficult job selling. It is a bit of a missed opportunity to cash in.
Kulusevski at Tottenham on a loan (5 million) with the obligation to buy at 35 in case of qualification to the Champions League and half of the appearances.