UPDATE: Kohta Nozane will replace Folger at this weekend's Japanese MotoGP.

Jonas Folger is to sit out this weekend's Japanese MotoGP and return home to Germany for medical checks.

The Monster Yamaha Tech 3 rookie has been struggling with fatigue since the Misano-Aragon races and doctors now suspect he has suffered a recurrence of the Epstein Barr virus.

Clinica Mobile medical staff examined Folger today at the Motegi circuit and recommended that he undertake further tests in Munich, with his participation in the next two 'flyaway' rounds in Phillip Island and Sepang now also in doubt.

"I came to Japan and was motivated for these three flyaway races, but I’ve been feeling really weak since the Misano and Aragon rounds," Folger explained. "On arrival here, I have been struggling with my energy levels, even leaving the hotel room was impossible for me, and unfortunately, I had to miss some Yamaha events, which I’m very sorry for.

"I met with Hervé [Poncharal] on Wednesday night and we agreed to go for a check with the doctors this morning. I met with Dr Charte and the Clinica Mobile team and they have advised me to return to Germany right away for a series of blood tests. I’ve had Epstein Barr virus in the past and it’s a possibility that this has flared up again and resurfaced, but we can’t be sure until I’ve had these tests in Munich.

"I’m really sorry for my whole team and Yamaha at their home race and would like to thank them for all their support. Also sorry to my personal sponsors, I appreciate them all standing by me at this difficult time. Now we must remain positive and aim to come back stronger."

Folger thus joins Jack Miller, who fractured his leg while training on a trials bike, in missing this weekend's Japanese Grand Prix.

The German's exit also means team-mate Johann Zarco is virtually guaranteed to win the 2017 Rookie of the Year title. Both have a best race finish of second, in the their respective home grands prix, with the Frenchman currently 33 points ahead with 100 still available.

Cycling star Mark Cavendish was diagnosed with the Epstein-Barr virus earlier this year.