Andy Murray is hoping to make the most of his last few years with Wimbledon approaching.
Briton admits performances in 2017 have not been good to remain atop of the ATP rankings.
Rafael Nadal became a 15-time Grand Slam champion after his victory at Roland Garros.
Federer lost in his first match back after a ten-week break in the Mercedes Cup in Stuttgart.
World number 307 beats 18-time grand slam champion in three sets in Stuttgart.
Mats Wilander believes Rafael Nadal's French Open win has restarted his campaign.
Nadal has played 10 tournaments thus far in 2017 - winning four titles.
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.