After Roland Garros, reigning French Open champion leads Swiss by almost 3,000 points in the Race to London.
18-time Grand Slam winner missed clay-court swing but will return to action in Stuttgart on Wednesday.
Nadal and Federer have won a combined seven titles this season including two Grand Slams.
Djokovic most recently crashed out in the French Open quarter-final.
Nadal won his 10th French Open title at Roland Garros in 13 visits.
Nadal has made seven finals and won four titles thus far in 2017.
Paul Annacone, who also worked with Pete Sampras, will join Swiss' coaching team for grass-court swing.
Spaniard won his 10th French Open crowd by beating Stanislas Wawrinka.
Rafael Nadal's win at the French Open has taken him to number two in the ATP rankings.
Wawrinka was outclassed by Nadal, losing the final in straight sets.
Mallorcan secures a historic 10th title at Roland Garros courtesy of dominant straight-sets win.
Federer is expected to return to action at the start of the grass-court season on 14 June.
Sharapova will miss the entire grass-court calendar.
Nadal is looking to achieve La Decima — winning the French Open for a record 10th time.
20-year-old Latvian produces a brilliant fightback to stun pre-tournament favourite at Roland Garros.
Spaniard remains on course to achieve 'La Decima' after comfortable straight sets win at Roland Garros.
2015 champion prevails 6-7 6-3 5-7 7-6 6-1 to seal second final appearance at Roland Garros.
Thiem is the only player to have beaten Nadal on clay in 2017 - in the quarter-finals of the Rome Masters.
Andy Murray face Stan Wawrinka in the first semi-final of the 2017 French Open on Friday.
20-year-old beats Timea Bacsinszky 7-6 (7-4) 3-6 6-3 in Paris.
Defending champion knocked out of French Open by Dominic Thiem.
Mark Petchey believes that troubled Serbian is "too good not to return to his best" after French Open exit.
World number one faces fellow three-time major winner Stanislas Wawrinka in French Open semi-finals.
Nadal and Federer have won three titles apiece in 2017.
Thiem is the only player to defeat Nadal on clay this year.
World number one wins 2-6 6-1 7-6 6-1 to reach last four for fourth time in a row.
The Austrian bested Djokovic in straight sets to reach second consecutive semi-final in Paris.
The defending champion accused of giving up after losing third set 6-0 at Roland Garros.
Djokovic appointed Andre Agassi as his new coach ahead of the 2017 French Open.
World number seven into his second straight semi-final at Roland Garros.