GREG Rusedski still shakes his head in disbelief when he thinks back to the first and only time he ever locked horns with Novak Djokovic. This was April 2006, Braehead Arena. Great Britain were taking on Serbia in a Europe/Africa Zone Group I second round tie.

While each team was armed with exciting young talent - Andy Murray partnered Rusedski in the doubles on the Saturday - the former US Open finalist distinctly recalls being taught a tennis lesson by this skinny little teenager from Belgrade. Ten years down the line, as these two teams prepare to battle again in a World Group quarter final in Belgrade next month, Rusedski sees a player who has all four Grand Slam titles in his kit bag and well on the way to supplant Roger Federer as the greatest of all time. Murray's misfortune at Wimbledon this fortnight is merely being the man whose task it is this fortnight to try to stop him. Assuming, that is, the Serb gets past James Ward on Monday.

"I sit here and talk with Tim [Henman] and some of the other guys and we look at Djokovic and ask 'how the heck do we beat this guy?'" said Rusedski, speaking at the Brodies Invitational event at Gleneagles. "I remember playing him at the Davis Cup in Glasgow in '06. I beat [Janko] Tipsarevic in five sets, then Andy and I lost in the doubles, then I played Novak the next day and I lost in the fourth. Everybody was telling me that his forehand breaks down and he gets a little tight. But I played just about as well as I could and I still lost to some 18 or 19-year-old kid.

"That 18 or 19-year-old kid is now 29 now and a hell of a lot better than he was back there," Rusedski added. "That was the only time I ever played against him, so it is a huge conundrum. Everybody thinks you have to be aggressive so his forehand breaks down a little bit, then you have to sustain. But he can hit winners from full splits. So he has taken the level up in terms of movement on a court from where [Roger] Federer had it."

Djokovic currently has an even dozen Grand Slam titles to his name, compared to the Swiss legend's 17. Whether or not he ever makes up that ground, Rusedski feels he already has a reasonable claim to be considered the best player in the history of the sport. Already armed with all four Grand Slam titles, adding Wimbledon and the US Open would mean that he has also completed an unprecedented six-in-a-row.

"He is possibly not only going to surpass Federer's record but do the calendar Grand Slam this year and no-one in the history of the game has ever done that - six in a row," said Rusedski. "I like to look at statistics and he has a winning record against Federer, a winning record against [Rafa] Nadal and a winning record against all his other main rivals at their peak. Federer, on the other hand, has a one sided record against Nadal and Andy had a winning record against him for a while too, until he lost six on the fly."

Should Murray make it to men's final day, few of the 15,000 fans will be huddled within Centre Court on men's final day will be rooting for a man who is more feared than loved, but Djokovic tends to thrive in the lion's den. Look at last year's US Open for instance, where he spoiled the party by taking down Federer in four sets. "The only people cheering for Novak that day were maybe a few Serbs in the crowd and his support team," said Rusedski. "The rest, maybe 22,000 were rooting against him. I saw him months later against Monte Carlo and told him 'that was the most amazing performance I have ever seen'. The guy is tough is nails."

With Ivan Lendl back in his entourage, having never so much as dropped a set against him on grass, Murray has reasons to be cheerful ahead of this year's Wimbledon. But even in the event that he goes down for a sixth Grand Slam final to the Serb at SW19 this summer, there is hardly any shame in that. As clearly the second-best player in the world right now, Rusedski feels that gives him equivalence to either Lionel Messi or Cristiano Ronaldo.

"Andy is special - he is our best player by far in the Open era," said Rusedski. "He is beating records that Perry had back in '36, he has been in all four finals of the slams, winning two of them, and he hasn't been far off in the others. I think people underestimate how great a champion he is. When he goes away he will get more credit than he does now.

"When you are talking about World No 2, then you are basically talking about Ronaldo and Messi every week, depending on what your argument is. If you were talking about European Championships or World Cup and you finished first and second every time then I think you would be pretty happy. Last year he was unlucky. Federer in the semis - a stinking hot day at Wimbledon. Federer served out his mind then the final was cold and windy. He was my pick to win the championship if he got into the final but he didn't make it that far."

Rusedski namechecks Dominic Thiem, Alexander Zverev - the conqueror of Federer in Halle recently - and Nick Kyrgios as three members of an emerging generation who could throw a spanner in the works this fortnight. But perhaps the biggest potential flaw in Djokovic's bid for world domination is the logistical difficulties of playing so many different tournaments in such short order.

"I think he [Djokovic] wants the calendar slam," said Rusedski. "And the Olympic gold medal. So he is going to just keep going. For me the gold is going to be harder because it is Brazil, with Zika, the travelling, all those things. So one thing is going to have to give - it is just whether it is going to be the calendar slam or the Olympic medal."