An ongoing elbow problem has plagued Djokovic, who accepted the need for surgical intervention after his fourth-round loss to Hyeon Chung at the Australian Open last month.

The 12-time grand slam champion ended his 2017 campaign prematurely, having been forced to withdraw from the quarter-finals of Wimbledon last July.

But the 30 year-old Serbian appears to be on the comeback trail, according to his latest Instagram post.

Taking to social media, Djokovic uploaded a picture of himself training in a gym, with the accompanying caption: "Working hard over here and the sweat is real. Thank you all for the continued support!"

Djokovic's woes are in complete contrast to evergreen rival and 20-time major winner Federer.

Aged 36, Australian Open champion Federer became the oldest man to occupy the top ranking en route to claiming the Rotterdam Open.