London:
Seven-time Wimbledon champion Roger Federer hailed ailing Nelson Mandela as "influential and amazing" on Monday as the anti-apartheid icon remained in a critical condition in a Pretoria hospital.
"He's been very influential, an amazing personality, you know, believed in something, had to pay a big price for it," Federer said of the former South African president, who spent 27 years in apartheid jails.
"Someone you can definitely look up to and that's very important for me. Clearly there's many that come and go, but he has been there for a very long time.
"And he's very much respected and loved. So we hope he does well here now in this process."
Federer was speaking after reaching the Wimbledon second round on Monday with a 6-3, 6-2, 6-0 win over Romania's Victor Hanescu.
The Swiss star has been a regular visitor to South Africa over the years where he has a charitable foundation.
The country is also the birthplace of his mother, Lynnette.
In 2011, Federer was voted second to Mandela in an international survey to find the world's most respected, admired and trusted personality.
Russia's 2004 Wimbledon champion Maria Sharapova also paid tribute to Mandela.
The 94-year-old was rushed to hospital with a recurrent lung infection on June 8.
"For someone with such a big name, who has touched so many people in this world, I think it's extremely sad to see him in that position," Sharapova said.
"I think it should be a celebration of what he accomplished in his life than a sadness, even though many people around the world are sad about it.
"He's extremely influential to so many people on a very positive level.
"I never had a chance in my life to meet him. But the people that have met him have said incredibly nice things about him," she said.