Wimbledon 2017: Roger Federer wary of main rivals despite their form and injury issues

One of Djokovic, Murray, Federer and Nadal has won every Wimbledon men's singles title since 2003

Roger Federer says 'Big Four' rivals Andy Murray, Novak Djokovic and Rafael Nadal will still pose a major threat to his Wimbledon hopes, despite questions around each of them.

The Swiss, 35, is the bookmakers' favourite to regain the title he last won in 2012.

Defending champion Murray is struggling to recover from a hip injury.

"If he's anything close to 100% physically, I consider him one of the big favourites," said Federer.

"It's that simple. It's the same for Novak and the same for Rafa."

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Djokovic, a three-time champion, won only his second title of the year in Eastbourne on Saturday after a poor 12 months by his standards.

Nadal returns to Wimbledon for the first time since 2015, after missing last year through injury.

Murray heads into the tournament without a win on grass this year after losing in the first round at Queen's Club, and was hobbling during practice sessions at the All England Club on Friday and Saturday.

"I think it's very even when we put it all out on the line," said seven-time champion Federer.

"Everybody has their own little story right now.

"For me, everything that happened sort of before - Queen's for Andy, whatever - doesn't matter so much.

"I feel like Andy's one of the best players in the first week at Wimbledon, so I don't worry too much for him there. He can play himself into shape hopefully for week two.

"Novak is just coming back from winning Eastbourne now. Rafa is coming in red hot from the clay.

"So I see it positive for them rather than negative in some shape, which I'm sure people will try to see that way."

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Nadal, 31, has not been past the fourth round at Wimbledon since 2011 and won the last of his two titles in 2010, but arrives fully fit and having just clinched a record 10th French Open.

"I am excited to be playing here again, in a tournament that I really love, I really enjoy playing," said the Spaniard, who plays Australian John Millman on Monday.

"At the same time, I tell you, it's a tournament that you can go out of very early.

"But if I am able to go through at the beginning, I think I am with confidence. I am playing well since the beginning of the season, so let's see."

Kerber's top spot at stake

Angelique Kerber has replaced Serena Williams as the world number one since reaching last year's final, but her form has slumped in 2017 and she is in danger of losing top spot after Wimbledon.

The German, 29, plays Irina Falconi of the US in her opening match.

"I'm starting from zero here," said Kerber. "My mind is just day by day here, like last year.

"I will not put the pressure too high. I'm already so long the number one, I will try, of course, to keep it.

Last year's Wimbledon runner-up Angelique Kerber has replaced winner Serena Williams as the world number one

"But at the end, I am here to play round by round and focusing only on my matches, not about the numbers or the rankings, the points I have to defend, or whatever."

Two-time champion Petra Kvitova will be the centre of much attention as she continues her remarkable comeback following a knife attack in December.

The Czech, 27, suffered lacerations to her playing hand and it was feared she might never play again.

On the contrary, Kvitova returned ahead of schedule at the French Open, and then won only the second tournament she played since her comeback, on the Birmingham grass last week.

"I'm not sure if it is the result of what happened, but maybe I feel a bit fearless because of what happened," said Kvitova, who opens against Johanna Larsson of Sweden.

"I find out what's important and what is not. Sometimes I'm thinking on the court that I already won the biggest fight, and if I fight in the match, it doesn't matter if I win the last point or lost. I will still be happy to play."