It's virtuely impossible for him to catch Nadal this year if my memory was correct.

Grand Slam:

Nadal won 1 and get in to 1 final and 1 quarters.
Djok get only 1 final and two semis.

Super 9 (master series now):

Nadal: 3
Djoc: 2

Other ATP series:

Nadal: should be 2 I think
Djok: don't remember

There are only two masters and ATP champ left. Djok has to won all of them and Nadal bascially get nothing (lose before semis or quarters) to surpass Nadal. I don't think he can, even tough there is a theoretical possibility.

He might get overconfident for a impressive run at US Open. However, that's against Fed's obviously underpar performance.