Wimbledon: Can anyone stop Roger or Williams?

I've never been a Rafael Nadal fan as such but my respect and admiration for the current World No.1 has increased almost exponentially over the past two Wimbledons. Unlike the vast majority of European and South American clay-courters who suffer from grass allergy, Rafa worked extremely hard to conquer his natural aversion to the surface, reaching a final and then dethroning Roger Federer at the latter's spiritual home.

It is, therefore, a genuine disappointment that Nadal will not be defending his title at SW1 this year. Unfortunately, there have now got to be doubts about his long-term future as a top player. His hustling, retrieve-at-all-costs style of play is brutally punishing on the knees and the onset of tendonitis at such a young age is not a good sign. Let's hope those fears prove unfounded and he can get back to the ATP tour as soon as possible because his rivalry with Federer has given tennis a much-needed shot in the arm. When was the last time the sport had two such thoroughly decent, down-to-earth characters dominating discussion?

Nadal's absence appears to have opened up the top half of the men's singles draw for Andy Murray, who has, despite being Scottish, taken over from Tim Henman as the home-crowd favourite. Murray's a better player than Henman ever was and has a good chance of becoming the first Briton since Lancastrian Fred Perry to win Wimbledon. He should have a relatively untroubled route through to the second week, although Taylor Dent looms as a potentially dangerous third-round opponent if he has recovered fully from the injuries that have blighted his progress over the past couple of years. Murray could then run into Stanislas Wawrinka or Marat Safin in Round 4, either of whom he should be able to get past with relative ease. His quarter-final, probably against Mikhail Youzhny or Nicolas Kiefer, might actually prove to be easier than the previous two rounds.

The top quarter, now devoid of the defending champion, could witness a showdown between Lleyton Hewitt and Andy Roddick, the best-credentialled grass-courters in that section of the draw, with the winner to meet Murray in one semi-final.

Nadal's injury worries put Roger Federer's amazing achievement of reaching 20 successive Grand Slam semi-finals into even sharper context. It's hard to see anyone challenging him in the bottom half. He may have a French Open Final re-match against Robin Soderling in the fourth round, although the Swede might find the serve-and-volley style of Feliciano Lopez - a highly uncommon trait for a Spaniard - too hot to handle in the third round. Federer's quarter-final could be against the exciting Frenchman Jo-Wilfried Tsonga, big-serving Croat Ivo Karlovic or the much-improved Fernando Verdasco of Spain. Looking further, I doubt Novak Djokovic will be Roger's semi-final opponent. It's more likely to be Tommy Haas, James Blake or Mardy Fish.

I'm predicting a Murray v Federer final with the Swiss genius having a tad too much grass-court nous and experience for the Scot.

A few years ago, there were doubts about the commitment the Williams sisters were showing towards the WTA tour. It appeared their off-field interests such as fashion - and even acting in Serena's case - were taking up too much of their time. Instead, they've seen off the now-retired Belgian duo of Justine Henin and Kim Clijsters and have just about quelled the Eastern European uprising as well, at least on grass.

Fortunately, Venus and Serena have been drawn in opposite halves. Is there anyone who can stop their path to the final?

In the top half, Venus' most difficult encounter could be in the fourth-round against Samantha Stosur. The Aussie, with a surprising run to the semis at Roland Garros, is in the form of her life. Having decided to concentrate on her singles career for the moment, her volleying skills, honed during several doubles title wins, will keep her in good stead. If Venus has an off-day, Stosur is more than capable of an upset.

The only player who looks likely to challenge Serena in the bottom half is Maria Sharapova. The US-based Russian has, however, been afflicted with injury this year and may not even get to her projected quarter-final meeting with the World No.2.

I can't see any of the Eastern Europeans mounting a serious challenge. Dinara Safina, the top seed at Wimbledon, was beaten by Thai veteran Tamarine Tanasugarn on grass in Holland last week. Vera Zvonareva might prove to be good enough to get to the semi-final from her quarter of the draw but is unlikely to trouble Serena if she gets there.

I'll take Venus to beat Serena in a repeat of last year's final.

The biggest surprise at this year's Wimbledon might prove to be the weather! It's forecast to be "largely fine and settled" in the first week, which will please the strawberry-and-cream vendors, not to mention the organisers, who will be happy to get through the early rounds on schedule.

Showers and even prolonged rain might dampen the second week but that might not be such bad news, as the main matches will be confined to the show courts by then.

The newly-built retractable roof on Centre Court is likely to be called into action in the latter stages. It'll be interesting to see what effect that has on proceedings.