Marc Marquez was forced to miss the Indonesian Grand Prix on Sunday after a crash during the warm-up.
The six-time world champion suffered a huge highside at Turn 7 and was left dazed on the ground after a heavy landing. He was taken to hospital for a check-up.
Race organisers later confirmed Marquez had suffered concussion and was not fit to start the first grand prix in Indonesia since 1997.
MotoGP medical director Dr. Angel Charte said: "Marc is fine. He had a high energy crash in the warm-up, which resulted in a head injury.
"Initially, we examined him here and then referred him to the hospital in Lombok. He underwent several radiological tests, which were negative.
"In agreement with the rider and the team, and due to the fact that this type of pathology requires a period of observation between 12 and 24 hours, the rider, the team and the MotoGP medical staff have decided to declare him as unfit."
The 29-year-old crashed twice during Saturday's qualifying session and had been due to start in 14th place, Franco Morbidelli's grid penalty pushing him up one spot.
The race at the Mandalika circuit was delayed by over an hour due to torrential rain, with television cameras capturing the dramatic moment that lightning struck the side of the track.
It had previously been decided to shorten the race to 20 laps as extreme heat had prompted concerns over tyre safety.
Reigning world champion Fabio Quartararo qualified in pole position ahead of Jorge Martin, with Enea Bastianini – who won the season opener in Qatar – starting in fifth.