I agree with McEnroe, this will affect Djokovic especially if he fails to win another Grand Slam, he is 33 years old after all and he will probably never catch Nadal who is in #2 in overall Grand Slam wins and Djokovic will probably be unable to catch Federer who is #1 on all time Grand Slam wins. If that remains then it will haunt Djokovic because both Nadal and Federer were his biggest obstacles in the US Open this year but both decided to not participate.
why would one grand slam make such a difference so that cannot catch Nadal or Federer at the top with the number of grand slams?
he would catch Federer with the number of weeks at the top of ATP list, and will fight with Nadal for number of grand slams, since it is more chances for Nadal to win another one/two RG, than Federer to win any tournament