Very very tough for Novak to get to Number 1. It will be either Rafa or Roger. Rafa is leading Novak by 4800 points (Which is 2 slams and a Masters 1000) in the ATP race. Since Roger did not play at all in the clay court season, he would have a chance if he wins Wimbledon. And I think Roger will for sure play most mandatory tournaments in the second half of the season.Unlikely as Federer will continue to be highly selective with the tournaments he enters. Let's also see whether Nadal's knees stand up to the stress of playing on hard courts and grass. I think it's quite likely he will have periods of fitness problems second half of the year.
Will be hard for Murray to stay number 1, as he has a ton of points to defend from now on. His chances of retaining his Wimbledon title don't look great considering the draw he has and his recent injury.
Could be a come-back time for Djokovich as he has few points to defend the latter part of the year.
http://live-tennis.eu/en/atp-race