Sydney, March 8 (IANS) Doctors finally have been able to solve world no.1 Roger Federer’s dilemma of why he felt sluggish at the Australian Open January. According to the doctors the Swiss had mononucleosis. “Roger found out he had mono, and didn’t know it. He found out a couple of weeks ago. That’s probably what was wrong with him,” Federer’s agent Tony Godsick was quoted as saying in The Daily Telegraph.

“He doesn’t want to make any excuses and take anything away from anybody. In hindsight, had (his doctors) known he had mono, they wouldn’t have let him play.”

Federer lost to eventual champion Novak Djokovic in the Australian Open semi-finals in January, then didn’t play again until this week, when he was upset by Andy Murray in the first round of the Dubai Tennis Championships.

Federer had not lost in the first round of a tournament since 2004. He was diagnosed with mononucleosis last month after seeing doctors in Switzerland and Dubai, Godsick said.

Mononucleosis is an infection caused by a virus. Symptoms include fever, sore throat, headaches and fatigue.

“This gave him a reason for why he wasn’t able to move and why he wasn’t able to recover,” Godsick said. “It was annoying for him to not have reasons for why his body wasn’t responding.”

Federer was cleared to start practicing five days before the start of the Dubai tournament.

Godsick said Federer is “over it now”, and will play Monday night against Pete Sampras in their exhibition match at New York’s Madison Square Garden.

Federer owns 12 Grand Slam singles titles, two away from Sampras’ career record. “I was feeling so great in December up until the moment I got sick, so this has been my problem the last couple weeks: really getting back on track,” Federer said.

“I haven’t practised and couldn’t really work out the way I wanted to, because you have to be very careful with mono.”