Roger Federer arguably is the most popular player in men's tennis today, with millions of fans worldwide. Novak Djokovic's father is not one of them.

Srdjan Djokovic never has forgiven the Swiss star for comments he made nearly 10 years ago about his son, who was ailing during a 2006 Davis Cup match between Serbia and Switzerland, according to Newsweek.

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And because of those comments, the sooner Federer exits the game, the better, the elder Djokovic said.

"Novak was just 19 at the time. He had a deviation of his sinuses and couldn't breathe," Srdjan told Newsweek. "And Federer tried in every possible way to disrespect him because of his breathing problem."

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The younger Novak defeated Stanislas Wawrinka in five sets, Newsweek added, but frequently had to call the trainer onto the court.

"Afterward, Federer said Novak's problems were a 'joke.'" Newsweek reported.

"He showed himself to be the best player in the world but not as a good person at that time," Srdjan said of Federer. "Nobody has ever treated Novak like this. I don't understand why Federer is still playing tennis. I don't know why he's still playing — he's already 34. "

To be fair, Federer wasn't the only one who thought Djokovic was soft early in his career.

Former No. 1 player Andy Roddick revealed that he almost came to blows with Djokovic after a quarterfinals match at the 2008 U.S. Open that came after Roddick accused the Serb of faking injuries, according to The Telegraph.

"Roddick had commented before the match on Djokovic's tendency to call for medical timeouts," The Guardian reported. "Roddick responded by suggesting that Djokovic was suffering from everything from a common coughing cold to anthrax and SARS.

"If it's there, it's there," Roddick said. "It's just a lot. He's either quick to call the trainer or he's the most courageous guy of all time."

Roddick later said he was on better terms with Djokovic.

Djokovic had that "soft" reputation early in his career, so perhaps Federer is just one of a long list of players with whom Srdjan has issues.

Even Djokovic's friends don't go unscatched.

Srdjan acknowledged that Andy Murray is a close friend but lacks the mental strength Novak now possesses.

Murray is a great, great talent, one of the biggest ever, and a big part of it is not being used, because his mindset is not calm," Srdjan says. "He gets frustrated very easily. When he's winning he has booming confidence, but once he starts losing, his mind turns around and he looks lost. He starts talking to his box, and this distracts his mind. If he learns to calm down, he will have a far bigger career than he has by now. I would love for Murray to achieve his potential."

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