Last Updated: Fri, 02 May 2008 17:00
Roger Federer has revealed that his patchy form this season could have been because he was playing with undiagnosed glandular fever.
The world number one has been struggling to reach the latter stages of tournaments in 2008 and lost out in the first major championships of the year in Melbourne.
Federer recovered from a five-set marathon against Janko Tipsarevic to beat two top players in Tomas Berdych and James Blake before losing to the Australian Open champion Novak Djokovic.
"The first time I got sick (before Christmas) I didn't think it was anything out of the ordinary," Federer said. "The second time (before the Australian Open) I thought it was food poisoning. The third time I thought something was wrong. That was when the doctors told me I had mononucleosis, but they said that by then it was almost over.
"By the time they'd done one more test they said it was over already, so it was never really a case of me saying: 'Oh my God, I've got mononucleosis'. It didn't really scare me.
"It wasn't as though I was in bed 24 hours a day for six weeks. I could play. That was what was so amazing. I was able to get up and play a five-setter against Tipsarevic at a time when apparently my mononucleosis was at its strongest."