i don't think its a lack of effort (unless we are talking about defending our box from open play) for me its why does fit into the team ?Dele is a Spurs success story. I see him as one of our own as much as Kane.
If he puts in the effort I can see him returning To being a key player for us. His pre-season has been pretty good.
if we had a real DM (Wanyama in his prime) then Dele could fit into 5 attacking plays, (eg Son Kane Moura, Dele GLC) but I see how to fit him into 4 attacking players