World number one Roger Federer dismissed suggestions his career was in decline and said he would use his recent defeats as motivation after recovering from an early-season virus.

The Swiss player was beaten in the first round in Dubai last week by Briton Andy Murray, his first match since losing to eventual champion Novak Djokovic in the Australian Open semifinals in January.

"In Switzerland there is a little too much speculation my career is over," the 26-year-old Federer told a news conference before his 6-3, 6-7, 7-6 victory over former number one Pete Sampras at Madison Square Garden. "People just need to know I'm healthy and happy and not miserable and down and out."

The 12-times grand slam singles champion, who competes at the Pacific Life Open at Indian Wells, California later this week, was told he had mononucleosis (glandular fever) after the Australian Open.

"Honestly, losses like this motivate me more than anything," said Federer. "Trying to come back, trying to prove I'm still the one to beat. I just want to show I can do it over and over again." The back-to-back defeats dented Federer's aura of invulnerability and fed the confidence of those younger rivals who have seen him reign as number one for a record 215 consecutive weeks.