Unpredictable and open-ended, this year's Wimbledon looks set to keep us guessing for two unmissable weeks

As everybody back at the IMG Academy in Florida knows, I’m rarely short of an opinion. However, I have a terrible confession to make. Wimbledon is just two days away and I have no idea who is going to win the men’s singles title this year.

Holy mackerel, did I just say that? People who’ve been reading my Wimbledon column for The Independent over the last 14 years ago know that I’m not exactly shy in coming forward, but I’m stumped when it comes to picking this year’s champion.

I can never remember going into a Wimbledon where there were so many question marks alongside so many players. To me there just isn’t a single stand-out favourite.

Andy Murray? He’s had an in-and-out year and now there’s a doubt about his fitness. Novak Djokovic? He hasn’t been at his best for quite a while either. Rafa Nadal? Well, the king of clay just hasn’t done it on grass in recent years and you never know how his creaky knees are going to be.

If I had to put my neck on the line I would have to go for Roger Federer, who has made such an astonishing comeback this year. Boy, he gives encouragement to all us veterans in our daily lives.

I know how much you Brits will be hoping that Murray can get his mojo back and it seems strange to be talking negatively about a guy who has won Wimbledon twice, is one of the great grass-court players of his time and is currently world No 1.

But you have to say that Andy is not in the shape he was going into this tournament 12 months ago. To me the big differences in his game compared with last year are his movement, which isn’t what it was, and his court positioning. He’s standing too far behind the baseline and just doesn’t look as confident as he did when he played further forward, taking the ball early, sneaking into the net and hitting great drop shots.

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I can only speculate as to why Andy hasn’t been at his best for much of this year, but I suspect that it may well be due to the shingles he went down with after the Australian Open. I wonder if in some way he is still paying a price for that, because it can be a big drain on your energy.

For me the biggest question mark at this Wimbledon hangs over Nadal. Holy smoke, if he’s going to play on grass like he’s played on clay this year, they could just hand him the trophy now and we could all head for the beach.

Rafa has added two big things to his game this year. His serve has improved and he seems to have added even more power to that incredible forehand.

He loves grass – remember, he got to the final at Wimbledon every year he played between 2006 and 2011 – but unfortunately for him his knees don’t. He’s had some shocking defeats on the green stuff in recent years.

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At this stage 12 months ago I thought Djokovic was just about the most perfect player of all time in that he didn’t have a weakness and did everything so well. Something has gone seriously wrong since then, but if anybody can get him back to where he was it’s Andre Agassi.

Was it really 25 years ago when I was Andre’s coach as he won the title here? The thing about Andre is that he subsequently sank much further than Novak has, but then got back to No 1. He knows what it takes to do that.

Nobody outside the “Big Four” has won Wimbledon since 2002 and if they are to maintain that stranglehold then it may well be down to Federer.

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Seeing him win the title in Halle last weekend, when he ran rings around a man 15 years his junior to beat Alexander Zverev, was like watching the clock turn back. He has so much energy he’s like a little kid who jumps up and down and runs around the house the whole day long.

I’ve been involved in sport for 60 years. I’ve loved watching Michael Jordan play basketball, Tom Brady play American football and Derek Jeter play baseball, but, as a spectator, I’ve had as much enjoyment watching Federer play tennis as I have watching any other athlete.

I love the way Roger never shows his emotions and always respects his opponents. He’s a champion off the court too with the time he spends with his family and the work he does for his foundation. Everyone in tennis should look at his example and learn from it.

Stan Wawrinka would complete a career Grand Slam by winning Wimbledon, but I’m not sure I can see that happening. He has a great game, including probably the most explosive backhand on the tour, but I don’t think he believes that he can be a champion on grass.

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There are plenty of other players I wouldn’t rule out. Milos Raonic’s movement is always a potential weakness, but in other respects he has everything you would want of a grass-court player.

Zverev has the look of a potential future champion and his brother Mischa has a great game for grass. None of the top guys will relish the prospect of facing Feliciano Lopez’s big leftie serve or John Isner’s cannonballs.

And finally I can’t let this moment go by without a word for 39-year Tommy Haas, who has been with me at the IMG Academy I founded in Florida for a quarter of a century.

Over the years Tommy and I have seemed to be in a head-to-head race: would my number of wives beat his number of operations? The lovely Cindi is my eighth wife, while Tommy went under the surgeon’s knife for the ninth time last year.

I’m thrilled that Wimbledon gave Tommy a wild card and nothing would please me more than to see him beat Ruben Bemelmans in his first-round match on Monday.

Nick Bollettieri, 85, has coached ten world No 1s over his career and founded what is now the IMG Academy in Bradenton, Florida in 1980. This is the 14th year in a row that he is writing a Wimbledon column for The Independent.