Tokyo,  India's badminton ace and 2016 Rio Olympics silver medallist PV Sindhu says she admires the class and elegance of American tennis legend Serena Williams and Swiss ace Roger Federer, and has great appreciation for Portuguese footballer Cristiano Ronaldo's skills.

"I don't have words, the way he (Ronaldo) plays, the skill, the technique he has is tremendous," Sindhu, who would be looking to change the colour of her medal in Tokyo to gold, told olympics.com.

Ronaldo recently won the Golden Boot at Euro 2020, following his five goals and one assist.

"Serena believes she can do it, being a woman, being a mother. She's done exceptionally well, she's a strong woman. Whereas, Federer, is another legend. Maintaining that level till now, at his age, is not easy. He's been there at the top," said the reigning badminton world champion.

At 39, Serena is the winner of 23 Grand Slam singles titles, while Federer, also 39, is still aiming for his 21st Grand Slam in singles.

Sindhu will begin her Olympic campaign against Israel's Polikarpova Ksenia on July 25. The Indian said that her training facilities at the Gachibowli stadium in Hyderabad had given her enough match practice for the Olympics.

"I understand a lot of people are saying we are lacking match time. But I don't feel that because we made such a scenario, such a situation, almost like match play. The Gachibowli stadium is almost like the Japan stadium, it is big, the air-conditioning, the shuttle control, and everything."