United Kingdom, Aug. 16 -- Novak Djokovic has secretly been battling an undisclosed health problem for "many years".

The 39-year-old tennis star made the admission after falling to his hands and knees and appearing to vomit during a shock defeat at the Cincinnati Open, with the 24-time Grand Slam champion becoming visibly unwell during his second-round match against Argentina's Thiago Agustin Tirante in Mason, Ohio, on Saturday (15.08.26.)

Novak won the opening set comfortably but struggled as the match progressed in hot and humid conditions, required medical attention and eventually lost 2-6, 6-4, 6-4 in his first competitive appearance since reaching the Wimbledon semi-finals last month.

Speaking to reporters afterwards, Novak said: ...