Tennis greats reveal doubts about breaking Wimbledon 'brick wall'

The gauntlet has been thrown down to the men's draw ahead of Wimbledon, with two former top tennis players declaring the big four are 90 per cent likely to reign again.

That prediction, from high-level coach Brad Gilbert and 18-time major winner Chris Evert, has come despite three of the four players arriving in London with significant hurdles to overcome.

While the rejuvenated Roger Federer heads into the grass tournament as the favourite, his three great rivals Rafael Nadal, Andy Murray and Novak Djokovic are no certainties to dominate.

Nadal won the French Open in style but has held off playing any lead-up tournaments even though his last four Wimbledons – 2012 through 2015 – have ended in the first week.

Murray reached the semi-finals at Roland Garros but is struggling with a hip injury after losing to Australian Jordan Thompson in the first round of Queen's last week.

Djokovic, meanwhile, bounced back from a second-round exit at the Australian Open to make the quarters in Paris, where he was dumped by a dominant Dominic Thiem in straight sets.

Yet none of that has put off Gilbert, who believes the draw is the next rung's biggest hope.

"I would think for that to happen, you know, a couple guys have to lose (early)," he told ESPN ahead of Wimbledon.

"I cannot see anybody outside beating three of those guys to win it, somebody having an amazing run, beating three of those guys ... I just think that’s the most difficult thing.

"If there is some help in the draw, a couple guys happen to lose, there’s an opening in the draw, maybe there’s a possibility. But you’re probably in the 90 percentile minimum of one of those four guys winning."

Evert lined up with Gilbert on that likelihood, poking holes in each second-tier contender's chance of victory.

The former world No.1 believes Stan Wawrinka, who was helpless in the French Open final against Nadal, remains the best hope.

"But Stan’s got to be more aggressive," she said.

"If he gets into an aggressive frame of mind, there’s a possibility. He’s an outsider. (Nick) Kyrgios is always dangerous, but mentally I don’t know if he can put together a lot of wins in a row yet.

"(Milos) Raonic is a question mark, (Alexander) Zverev. I mean, you got some dangerous players that could upset one of those top four. I just don’t know if they can do it consistently. It’s like a brick wall, I think, to get through those four players."

Gilbert believes Nadal, who he says never looked better than in the recent clay season, is especially vulnerable.

The 55-year-old Californian complimented the Spaniard's serve and forehand, which is "back to being devastating", but the conditions in the first week may be his undoing.

"If he can get through that first week, then I think he can get a lot of confidence going into the second week," he said.

"I think his game plays a lot better when the conditions are warmer and the ball bounces higher for him. I think his game is more effective."

Added Evert: "He’s stepping in, moving in. When he wasn’t confident, he was six to ten feet behind the baseline on every surface, just counterpunching, just retrieving.

"He’s so confident now, I think that is reflected in the way he’s playing, coming into the baseline. He’s coming to the net a lot more, even on the clay.

"It was as natural as anything for him to hit a ball, come in, volley away a winner. We haven’t seen that in Rafa."

While both Gilbert and Evert have some confidence in Murray returning to his 'A game' in front of the London crowd and on his favourite surface, they came back to the settled Federer.

With rest through the clay season and a confidence in his training methods, it won't surprise either if the Swiss great lifts a 19th major trophy on July 16.

"I think it all looks good at the moment for Roger," Gilbert said.