MONTE CARLO: Roger Federer may have lost the tag of world No 1 but he is still a formidable opponent, several top players said on Monday.

The usually-composed Federer, who has yet to win a tournament in 2009, broke down in tears after losing the Australian Open final to the top-ranked Rafael Nadal in January and smashed one of his rackets in this month's Miami Masters.

"I found it strange he broke his racket in Miami, he who always keeps calm," world No 3 Novak Djokovic told reporters at the Monte Carlo Masters. "But these things happen when you are frustrated on the court.