Wimbledon 2017: Andy Murray as impressive as ever but his fitness really is a worry going forward

Nick Bollettieri casts his eye over the world No 1's opening of the tournament on centre court

Winning a Grand Slam title is the toughest task in men’s tennis. Man, winning seven matches over the best of five sets in the space of two weeks tests to the very limit your tennis, your mental strength and your physical capacities.

Andy Murray’s tennis was as stunning as ever in his opening match against Alexander Bublik and mentally he coped superbly with all the pressures of opening the tournament as the defending champion, but I have worries about whether his fitness will stand the test.

Holy mackerel, you would never have guessed he had a problem with the way he chased down some of Bublik’s drop shots and hit winning passing shots on the run.

However, I was concerned with what I saw between points. The sore hip that has troubled him for the last week or two appeared to be troubling him again and there were times when he seemed to be limping.

Beating a guy ranked No 135 in the world in three sets is one thing, but how will your man cope if he gets drawn into a long five-setter against one of the big guns later in the tournament?

Murray has got to where he is by running down every ball and chasing down every apparently lost cause. What he mustn’t do is retreat behind the baseline in the way he used to do. His improved court positioning is what has taken him to the top of the world. If he starts to move backwards he’ll quickly find himself in big trouble.

I certainly enjoyed watching Bublik. He’s one of a strong group of young players who love to go for their shots and play without fear. What it is to be young!

I was very happy to see Venus Williams win but sad to see her so upset afterwards. She is clearly going through a tough time at the moment and I just hope she is able to focus on her tennis.

Tuesday’s match of the day

I like the look of the meeting between Caroline Wozniacki and Timea Babos. Although I think Wozniacki will edge it, this could be a terrific match.

Babos’ biggest weapons are her serve and her backhand. The Hungarian is also a very good doubles player. I think she’ll need to get into the net to finish off the points early because Wozniacki makes you hit more balls than almost anyone on the women’s tour.

Wozniacki misses very little and to beat her you always need to do more than just put the ball back in play. You have to go for your shots, because if you just keep getting the ball back into play she will outlast you.

Wozniacki faces a tough opener at SW19 (Getty)

She has been coached all her life by her father, who should be very proud of what she’s achieved. I often think he should play poker because he has such an expressionless face. It’s always hard to guess what he might be thinking.

Tales from the IMG Academy

Some people tell me there’s no way Andre Agassi can turn Novak Djokovic’s fortunes around unless they spend much more time working together. All I would say is that when I was coaching Andre he showed me time after time how quickly things can change. After being No 1 in the world he dropped out of the top 100 and then worked his way back to the top again.

Take Andre’s victory at Wimbledon 25 years ago, which remains one of the absolute highlights of my career. Just a few days before the tournament Andre phoned me at 3am to suggest that we practise at Boca Raton for two days before heading to Wimbledon.

When we met up at Boca it was the first time we had worked together since the French Open. We found two green hard courts, which we pretended were grass, and after just half an hour of hitting Andre said he was ready for Wimbledon. Who was I to disagree?

I didn't think Agassi had a chance of winning

On arrival in Britain Andre was asked by a reporter how his training had been going. Andre winked at me and told the reporter that we had been working hard at Boca for two weeks.

Hell, at the start of the tournament I thought Andre had more chance of becoming chairman of the All England Club than men’s singles champion. Andrei Chesnokov pushed him hard in the first round, but from that moment onwards Andre went from strength to strength, and the rest is history.

A tip from the top

I’m going to give you a piece of advice each day on how to improve your own game. Here’s one about your return of serve. The safest place to hit a return is always cross-court because you’re hitting over the lowest part of the net. That’s also the longest distance between the lines, so it gives you the biggest margin for error. When you’ve sounded out your opponent you might want to start mixing up your returns, but your first aim has to be to get the ball back in play.

The perfect tennis player

Each day during Wimbledon I’m going to build my picture of the ideal tennis player by looking at a different aspect of the game. Let’s start with the forehand.

Ivan Lendl, Jim Courier, Andre Agassi and Steffi Graf all had great forehands. I’d also have to mention Jimmy Arias, who developed a great forehand when he was with me at the academy. Nor should we forget the two-handed forehands of Monica Seles and Pancho Segura.

Federer's forehand is the best one around (Getty ) (Getty)

Today Serena Williams has a magnificent forehand, but I don’t think I’ve ever seen anyone hit the ball with such pure power as Juan Martin del Potro. Holy mackerel, his forehand’s been timed at 105mph!

Rafa Nadal and Jack Sock also have excellent forehands, but for consistency, reliability and great hitting I have to go with Roger Federer. His movement is so good that he can hit those devastating forehands from almost anywhere on the court.