His bad performance this season may be caused by his low motivation to play. I am sure he is very disappointed with Tottenham management. In the previous transfer window, he really wanted to leave. Unfortunately, Tottenham management didn't allow him to leave. That situation must influence his mood in playing, he didn't play with a good motivation to score.
Yep, He wanted so badly to join Manchester City and he almost missed the preseason because he does not want to train for Spurs anymore.
I think he will go to Manchester next year and Tottenham will go for Vlalovich, already wanted from Paratici at Juventus.