Novak Djokovic’s latest Grand Slam campaign ended in painful fashion at the US Open on Monday, with the 39-year-old admitting he is uncertain about how much longer he can continue competing at the highest level after a physically exhausting defeat to Mariano Navone of Argentina. The 24-time Grand Slam winner battled through a series of fitness problems before eventually falling 7-6, 5-7, 6-4, 2-6, 6-1 to Navone in the opening round at Arthur Ashe Stadium.Novak Djokovic addressed his future after suffering a shock defeat (Getty Images via AFP)Djokovic’s condition deteriorated as the match wore on. Humid conditions appeared to take a significant toll on the Serbian, who was visibly exhausted and struggled to maintain his intensity during the five-set contest. He was seen using an ice bag on his head during the match, after rain forced the roof to be closed.The physical difficulties became particularly severe in the third set when Djokovic vomited on court. He received medication from a tournament physiotherapist and fluids from his team before attempting to continue.Also Read: Novak Djokovic loses first-round match of a Grand Slam after 20 years; crashes out of US Open“The vomiting, the gagging, it’s a serious problem. Then my whole body started to give way, with cramps and pain. In the end, my back and shoulders also gave out, and I couldn’t finish the match. I was a break up in the fourth set, but I had already been struggling a lot from the fourth game onwards,” Djokovic told reporters.Djokovic’s frustration and exhaustion were evident at the conclusion. The Serbian broke down in tears, while his comments afterwards suggested that the physical demands of competing at the top of the sport are becoming increasingly difficult to ignore.“I don’t know how I can solve it. At the moment, I don’t want to go into too much detail. I’m just trying to understand what’s going on and how much longer I can keep going like this,” Djokovic said.Did he want to quit?The former world No. 1 acknowledged that the possibility of stopping had crossed his mind during the contest, but he chose to continue fighting rather than retire from the match.The defeat also ended one of the most remarkable records in Grand Slam tennis. Djokovic had won 78 consecutive first-round matches at major tournaments, with his previous defeat at that stage coming against Paul Goldstein at the 2006 Australian Open.“Yes, I did,” Djokovic replied when asked whether he had considered giving up.“But then I won one set and then another. At that point, I said to myself: ‘OK, maybe there is a chance.’ I didn’t want to give up in the fourth or fifth set. I wanted to finish the match," he added.His latest setback also brought his pursuit of a record-extending 25th Grand Slam title to an abrupt conclusion.