Roger Federer has admitted that he will have to be at his best to overcome Jo-Wilfried Tsonga in the French Open quarter-finals on Tuesday.
Tsonga will be hoping to end France's 30-year wait for a male champion, but Federer has impressed in the early stages of the competition this year.
"He's dangerous, dangerous for everybody ranked in the top four in the world. He's proved his worth in the past. I know him very well. There's no real secret between us tennis wise," Federer told reporters at a press conference.
Tsonga has already beaten the Swiss at Wimbledon.
