Two-time world champion Fernando Alonso brought the morning session on the final day of the second pre-season test in Barcelona to a premature end when he crashed the McLaren-Honda MP4-30.
The Spaniard had managed just 20 laps on another troubled morning for the struggling giants, who lag well behind every other team on the grid in terms of mileage with the start of the season less than a month away.
Alonso received medical attention at the circuit and was then airlifted to hospital.
"Fernando Alonso's McLaren-Honda car left the track at turn three, causing the right-hand side of his car to strike the wall," McLaren said in a statement.
"Fernando was driven to the circuit's medical centre where the circuit's doctors gave him first aid.
"He was conscious and spoke with the doctors.
"However, as per usual procedure in such circumstances, he was then airlifted to hospital where he is undergoing precautionary checks."
Jenson Button was already scheduled to take over from Alonso for the afternoon session having been very limited in his running on Thursday and Saturday due to a faulty seal.
It was a much more positive morning for the other Spanish driver on show as rookie Carlos Sainz Junior was fastest in the Toro Rosso in a time of 1min 25.604.
Sebastian Vettel was second quickest for Ferrari, whilst Mercedes continued their mileage marathon in testing as Nico Rosberg logged another 68 laps despite an early spin-off into the gravel.
Results from the morning session on day four of the second pre-season test in Barcelona:
1. Carlos Sainz Junior (ESP/Toro Rosso) 1:25.604 (59 laps)
2. Sebastian Vettel (GER/Ferrari) 1:26.312 (59 laps)
3. Nico Hulkenberg (GER/Force India) 1:26.591 (33 laps)
4. Nico Rosberg (GER/Mercedes) 1:26.782 (68 laps)
5. Fernando Alonso (ESP/McLaren) 1:27.956 (20 laps)
6. Romain Grosjean (FRA/Lotus) 1:28.029 (40 laps)
7. Daniil Kyvat (RUS/Red Bull) 1:28.149 (38 laps)
8. Valtteri Bottas (FIN/Williams) 1:28.171 (52 laps)
Source: AFP