#1 Stefan Edberg
Stefan Edberg enjoyed a famous rivalry with Djokovic’s current coach Boris Becker during their playing days and the Swede has proved himself capable of rivalling Borg even in coaching.
When Federer sought the help of Edberg in 2014, he was going through a lean period by his lofty standards. The 17-time Grand Slam winner rediscovered his touch soon and even reinvented his serve-and-volley game though he failed to win a Grand Slam.
Edberg’s influence on Federer was evident in the way went about managing his ageing body while still maintaining his game. In fact, a lot of work Edberg did was to help Federer adapt his mindset.
Federer described Edberg's role as "more of a mentor than a coach", and it might just be what Novak needs. A change in mindset might be the perfect tonic for Djokovic right now, and who better to administer it than Edberg.