Cape Town - World No 1 Novak Djokovic's father has slammed his son's tennis rivals Roger Federer and Rafael Nadal, claiming they are jealous of Novak's success. In an interview with the Serbian daily Kurir, the outspoken Srdjan Djokovic said Federer and Nadal have not taken Djokovic's rise to the top too kindly. He said his son is as classy a loser as in there is in sports, unlike Federer and Nadal.“Federer is perhaps still the best tennis player in history, but as a man he’s the opposite," said Srdjan. "He attacked Novak at the Davis Cup in Geneva (in 2006), he realised that he was his successor and was trying to discredit him in every way. Novak’s success is an amazing thing and something that one cannot understand.”There has been bad blood between the Federer and Djokovic clans in the past. In the abovementioned Davis Cup tie, Federer questioned Djokovic’s use of medical timeouts. In a later match in 2008, Federer told the Djokovic family to “be quiet” while he was serving.Djokovic was well-known early in his career to quit matches when it became too taxing physically. His mother, Dijana, also once infuriated Federer when she said “the king is dead” after Djokovic beat Federer in the 2008 Australian Open semi-finals. Federer has a 16-13 winning record against Djokovic.Srdjan also had harsh words for Nadal, who has a 20-15 winning record against Djokovic but has struggled in recent years against the Serb. Djokovic has won eight of their last 12 meetings, including a seven-match streak from 2011 to 2012.“Nadal was his best friend while he was winning. When things changed, they were no longer friends. This is not sport. This is what Novak has in him, but others don’t," said Srdjan.Srdjan had nicer words for Andy Murray, Djokovic's other main rival on the ATP Tour."I have never, not even for a second, felt jealousy from Andy’s family," said Srdjan. "They cannot be best friends as they fight for the most important titles, and lot of money. But they are more than correct rivals". Srdjan is sure that after they finish their professional careers, Novak and Andy will be great friends.