Monster Yamaha Tech 3 rider Jonas Folger will miss the 2018 MotoGP season as he continues to struggle with Gilbert Syndrome.
The German was unable to ride at the end of the 2017 campaign due to illness and discovered that he has a rare strain of a common genetic disorder, preventing the liver from processing toxins effectively.
Folger, a rookie last season, revealed last November that his body had "shut down completely" due to the condition and says he will not be physically or mentally fit to compete this year.
"I'm incredibly sad to be saying this, but I will not be racing MotoGP in 2018," says Folger. "I wasn't able to make the improvements I was hoping for, and at this stage I don't feel able to ride a MotoGP machine at 100 per cent.
"I'd like to thank everyone involved, but especially the Monster Yamaha Tech3 team, Yamaha Factory Japan, Monster Energy, HJC, IXON, Forma Boots and Rudy Project. I hope to be back one day and want to thank you all for your ongoing support."
Team manager Herve Poncharal said: "Last night (Tuesday) I received a call from Bob Moore, Jonas Folger's personal manager. I couldn't believe what Bob was telling me on the phone, that Jonas Folger has decided not to race the 2018 MotoGP season because he doesn't feel 100 percent mentally and physically recovered.
"It is still very difficult for me to believe, that he's not going to race with us in 2018, especially because he has been somebody I had lot of faith in and I was sure we would reach top level together this year.
"I completely respect his decision, although it's hard to swallow. Yet, I will try to find a solution for a replacement rider, which is a very difficult mission, as all of the fast riders are already contracted.
"But as always in racing we need to be proactive, inventive and hopefully we can make someone very happy. We will keep all of you informed about the evolution of the situation."