Zurich  - The Andre Agassi crystal meth revelations, to be fully explained in his autobiography next month, have come as a shock to world number one Roger Federer.

The top seed at his home event from Monday in Basle told local media that Agassi's confession to have used the drug crystal meth during a low points in 1997 was a stunner.

"It was a shock when I heard the news," said Federer at a sponsor function. "I'm disappointed and I hope there are no more such cases in future. The sport must stay clean."

He added that the now-retired 39-year-old Agassi "has done a lot for tennis. He raises millions of dollars for his foundation for disadvantaged children."

In Madrid, world number two Rafael Nadal joined in, calling the revelations "terrible."

"Why is he saying this now that he has retired? It damages the sport, it makes no sense. I'm the first one who wants to make sure tennis is clean."

Americans give their compatriot the benefit of the doubt, with Andy Roddick calling the 39-year-old "my idol."

"I'll judge him on how he has treated me and how he has changed the world for (the) better," said Roddick on his Twitter page. (dpa)