The father of Novak Djokovic has said Andy Murray must remain calmer in matches if he is to fulfil his potential.
Murray holds two grand slam titles and almost single-handedly secured Davis Cup glory for Great Britain in 2015 with a series of impressive performances.
However, Murray has lost 11 of his last 12 meetings with Djokovic - including the last two Australian Open finals - and would appear to face a huge challenge in closing the gap to the dominant world number one.
In an interview with Newsweek Europe, Srdjan Djokovic hailed Murray as "a great, great talent ... one of the biggest ever," but added: "A big part of it is not being used, because his mindset is not calm. He gets frustrated very easily.
Djokovic senior continued: "When he is 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."
Srdjan Djokovic spoke of the bond between his son and Murray, who have known each other since childhood, stating: "They are amazing friends. At the moment they cannot be good friends outside of tennis, because they are rivals, but once they have finished their careers they are going to be much better friends than they are today."
However, he was less complimentary towards 17-time grand slam champion Roger Federer, accusing the Swiss of showing a lack of respect to Novak during a Davis Cup tie in 2006.
"When Serbia played Switzerland in Geneva, Novak was just 19 at the time. He had a deviation of his sinuses and couldn't breathe," added Srdjan Djokovic.
"He had a problem with staying in long matches and long points and Federer tried in every possible way to disrespect him because of his breathing problem.
"He showed himself to be the best player in the world, but not as a good person at that time. Nobody has ever treated Novak like this.
"I don't understand why Federer is still playing tennis. Why does he still play? He's already 34."
On his son's future, Srdjan Djokovic added: "I believe he will be the best tennis player in history. Surely he will be one of the best sportsmen ever. He can win another 10 grand slams."