McLaren's Fernando Alonso will miss the season-opening Australian Grand Prix on 15 March on medical advice.
Doctors say the 33-year-old Spaniard is not injured following his crash in testing on 22 February, but advised him not to race in Melbourne because of the risk of suffering a second concussion.
Sustaining a concussion injury while still affected by a previous one can have serious consequences, which can extend to prolonged coma or even death.
Kevin Magnussen will replace Alonso.
The 22-year-old Dane is the team's reserve driver.
Alonso lost control of his car at 215km/h (133.6mph) in his crash at the Circuit de Barcelona-Catalunya.
He hit the wall and suffered two impacts on his head, after which he was flown immediately to hospital, where he was kept for three nights.
A McLaren statement said a series of medical tests and scans found Alonso had "no medical issue" and was "entirely healthy from neurological and cardiac perspectives alike".
But it added doctors recommended the two-time world champion should "for the time being" limit activity that could result in another concussion "so as to minimise the chances of second impact syndrome".
Alonso receives medical assistance after crashing at the Circuit de Barcelona-Catalunya
Second impact syndrome is where a patient suffers a second concussion before the first is entirely healed, and 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.
Alonso said in a video posted on YouTube last Friday that he was "completely fine" and was looking forward to getting back in the car "very soon".
McLaren said his doctors were "supportive" of his ambition to return to the cockpit in time for the second race of the season in Malaysia on 29 March.
It added he had already restarted his physical training, with his doctors' backing.
McLaren have suffered poor reliability in their pre-season testing programme and have admitted they expect to struggle for competitiveness in the first four races of the season.