BEIJING, August 6, 2008 (AFP) - Roger Federer and Rafael Nadal both kept their heads down after training at the Beijing Olympic tennis venue on Wednesday leaving former world number one Lleyton Hewitt to sing their praises.

Federer, who seems not to have taken his imminent demotion to second best player in the world too well, dismissed waiting journalists' questions with a cursory nod of the head after two hours of practice with Swiss team-mate Stanislas Wawrinka.

The determined current number one - until Nadal takes over top spot on August 18, the day after the Olympic final - then went off centre court to continue practising on one of the outside courts, dismissing the punishing heat and humidity in a bid to find his waivering form.

Nadal did not talk to journalists either but his reluctance was more likely due to a pre-arranged evening press conference appointment.

Meanwhile, Hewitt, a winner of two Grand Slam titles, praised Nadal's elevation to the world's top spot but warned against writing off Federer.

'Rafa has taken over the mantle. No other player on earth could have done what he did to Federer in the French Open final. He destroyed him. It was amazing and then to take his Wimbledon title, too,' said Hewitt on Wednesday.

'He deserves to be number one. Roger hasn't been playing as well as he can. But the French Open and the Olympics are about the only highlights missing so there's no doubt he'll be trying his best here.'

On Wednesday, Nadal took part in two practices but shorter ones than his Swiss rival.

He looked every bit the new world number one in a practice match against Chilean Fernando Gonzalez.

That only lasted a half hour but Nadal then came back on court later on in relaxed mood, driving up on a little electric-operated scooter, displaying none of the solemn seriousness of his main gold medal rival.