Novak Djokovic says he was suprised by news of Roger Federer's knee surgery and hopes to see his rival back on court soon as the sport needs him.Federer said he would miss a number of tournaments, including the French Open in May, after undergoing keyhole surgery in Switzerland last week.Federer suffered a groin problem in his Australian Open quarter-final win against Tennys Sandgren and his movement appeared hampered in his defeat to eventual champion Djokovic in the semi-finals."It was a surprise, to be honest," Djokovic told reporters ahead of the Dubai Duty Free Tennis Championships."I knew he was struggling with an injury in the Australian Open. But no one knew really what was the injury, what is the extent of that injury." Djokovic, who won his 17th Grand Slam title in Melbourne, underwent an elbow operation in 2018 in a bid to cure an injury that has troubled him for a long time."I really don't like to see anybody going through surgery. I've been through that once, and hopefully the last time in my life," he said.

" Roger is Roger - this sport needs him."

Djokovic also revealed that he, Federer and Rafa Nadal have a WhatsApp group and said the 'Big Three' of men's tennis get along very well."We are all active, and we are not active as well," he said of the chat group. "When we are active everybody responds. We got it, we get along very well, I think we know, there is tremendous respect for each other, privately and professionally."As long as this is the case, everybody benefits from that and the sport as well."The Serb is yet to lose a match in 2020 having led Serbia to victory in the inaugural ATP Cup team event in Australia followed by his eighth crown in Melbourne.The 32-year-old said it will be a fresh start for him when he opens his bid for his fifth title in Dubai, and first since 2013, against Tunisian wild card Malek Jaziri."Yes, there is room for improvement. That's my biggest motivation," he said. "That's probably one of the biggest reasons why I keep on playing this sport and why I put a lot of effort and dedication every single day."I feel that tennis is a great place for me to improve not just in tennis but also as a human being to build my character."