McLaren's Fernando Alonso will miss the season-opening Australian Grand Prix on 15 March on medical advice.
Doctors have advised the 33-year-old Spaniard, who crashed in testing on 22 February, not to risk a second concussion by racing in Melbourne.
Alonso tweeted: "It will be tough not to be in Australia, but I understand the recommendations."
The two-time champion's place will be taken by 22-year-old Dane Kevin Magnussen, McLaren's reserve driver.
Magnussen tweeted: "Shame about the circumstance but still I'm so excited to be racing in Melbourne."
Alonso was driving at a speed of 215km/h (133.6mph) when he lost control of his car at the Circuit de Barcelona-Catalunya.
He hit a wall, suffered two blows to his head and was immediately flown to hospital, where he was kept for three nights.
McLaren said a series of medical tests and scans found that the former Ferrari driver had "no medical issue" and was "entirely healthy from neurological and cardiac perspectives alike".
But a team statement said doctors had recommended he should limit his activity "so as to minimise the chances of second impact syndrome".
Second impact syndrome occurs when a patient suffers another concussion before the recovering from the first.
It can result in raised intra-cranial pressure, prolonged coma and can be fatal.
Doctors say recovery from concussion cannot be predicted and that it varies from patient to patient.
In a YouTube post Friday, Alonso said he was "completely fine" and looking forward to getting back in the car "very soon".
McLaren said his doctors were "supportive" of his desire to return in time for the second race of the season in Malaysia on 29 March.
They added he had already restarted his physical training, with the backing of his doctors.
McLaren have suffered poor reliability in testing and say they expect to struggle for competitiveness in the first four races of the season.