"I have spent most of the last month in and out of my doctor's office getting tests done, trying to figure out what is going on," Reed said.

Reed, 28, from Kurri Kurri in New South Wales, said he had been baffled by his inability to race to his normal level.

"Knowing that I have worked hard during the week on and off the bike, each weekend I head to the race excited to get out there and get some wins on my Monster Kawasaki - ready to defend the No.1 plate that is on my bike," he said.

"The team and bike are prepped and ready on race day, and then I'm unable to race like I normally can.

"For most of this outdoor season I have been frustrated and questioning every part of my program, wondering why I am unable to race to my full potential.

"It's embarrassing riding with the No.1 plate on and not battling at the front.

"I don't take it lightly, and I knew I had to get to the bottom of my issues.

"Finally I got my results back from the doctor and I have Epstein Barr virus.

"I know some other riders have had it, and I never thought I would be sitting here saying the same thing.

"It explained my fatigue issues on the track.

"I knew it wasn't my fitness, but I was struggling to finish motos."

Reed said that his problem had reached a point where it was "dangerous for me to be out there".

"My doctor, team and I have decided that I need to be off the bike for a while to try get this handled," he said.

"I am really disappointed to be out again.

"This year has been a personal worst for me.

"I have often been referred to as Mr Consistent, but this year has been far from that.''

Reed said that he would return to racing as soon as possible.

"I'm not ready for retirement," he said.

"I want a few more championships indoors and out."