Former Wimbledon great Bjorn Borg believes world number one Roger Federer [Images] is only third favourite to win the grasscourt Grand Slam this year.

Federer is aiming for a sixth consecutive Wimbledon title but Borg, champion five times in a row from 1976-1980, thinks the Swiss will have his work cut out.

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The Swede also said he will not be surprised if Federer chooses to retire next year.

"I pick Rafael Nadal [Images] as winner and my second choice is Novak Djokovic, my third is Roger," Borg was quoted in British media on Thursday.

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"For (Roger) to beat those guys at Wimbledon he needs to play much better than he did last summer. He knows he will have to play some unbelievable tennis to win again. This is the most open Wimbledon for years."

Borg, who retired in his mid-twenties, thinks Federer can overhaul Pete Sampras's record of 14 Grand Slam titles -- if he keeps playing.

"I wouldn't be at all surprised if Roger came out next year and said: 'I'm not going to play tennis any more', Borg added.

"It probably won't happen but if Roger decides to retire that wouldn't shock me at all. People expect him to win all the time and that is mentally and physically tiring.

"It's not going to be like before when he used to win nearly every match he played. That time has gone."

Federer, beaten in the semi-final at this year's Australian Open by Djokovic and in the French Open final by Nadal, has won 12 Grand Slam titles.

"He wants to break the Sampras record and I think he will if he wants to continue playing tennis," Borg said.

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