Mercedes driver George Russell says the new Madrid circuit is "very high risk" after British rookie Arvid Lindblad crashed in Friday practice at the Spanish Grand Prix.
Racing Bulls' Lindblad was the only driver to have an accident, although several drivers brushed the wall while learning the new Madring circuit.
The 19-year-old lost control into Turn 13, and slid sideways into the wall, damaging his front and rear suspension and breaking his front wing.
Despite that, Lindblad ended the session an impressive fourth fastest, just 0.228 seconds behind pace-setter Kimi Antonelli's Mercedes.
Ferrari's Charles Leclerc and Lewis Hamilton were second and third fastest, just over 0.1secs behind Antonelli.
Russell was fifth fastest ahead of Red Bull's Max Verstappen and McLaren's Oscar Piastri. World champion Lando Norris did not set a time in his McLaren because of a gearbox problem.
Russell said: "Without doubt, it is a circuit of very high risk and probably all the drivers were giving that bit of margin today. Let's see tomorrow."
Briton Lindblad was encouraged by his pace before his accident.
He said: "It's not an easy track, so we're all pushing to find the limits. It's new for all of us and I just made a bit of mistake and overdid it a little bit in Turn 13.
"A bit of a shame, I apologised to the mechanics and team because it's a bit of extra work for them.
"But looking at the big picture, it's been a good day. We're very fast, I was running P4 on merit. I was only 0.2secs from P1 which is really strong."
Russell said the drivers had experienced significant problems with tyre degradation on the new track surface.
"The grip is very high but you are sliding quite aggressively," Russell said. "With the (tyre) deg we had in P1, a six-stop race would be the fastest way. P2 was slightly better. I'm sure the race will be better again but that is the biggest question mark."
Leclerc said: "The track is very exciting, very challenging, and it's a street track as well and these are the tracks I normally quite enjoy, and this is no exception to that.
"It was really nice to be driving on this new track. There is still a lot of work to be done and I expect it to be one of the most challenging qualifying sessions of the year, being such a commitment track.
"Qualifying is for sure going to be the key moment of the weekend because in P2 it was extremely difficult or impossible to overtake so most of the performance this weekend will be based on the qualifying."
Russell, who heads into the weekend trailing Antonelli by 66 points in the championship, had before practice descried the Madring as "less margin than Monaco, purely because of the speed".
He said: "In Monaco, the walls are closer, but because you're going far slower, if you make a mistake, you're not into the wall as quickly, and you can recover it sometimes, a small lock-up.
"There's a lot of really fast corners, but the barrier is kind of like coming back on to the track. So, if you are to go wide and hit the wall, you're not hitting it kind of at the same angle as the car is going. The wall is sort of coming in at you."
Russell singled out Turns Five, Seven and 17. Leclerc went off into the run-off area in 17.
Russell said: "Another element of the challenge here, which probably won't cause major crashes, but I think there'll be a lot of lock-ups.
"You've got three corners where you're turning and braking, and if you lock up, the wall is right in front of you, which is very reminiscent of the corner in Baku, Turn 15. You know, the one down the hill where a lot of people go off."
There is also a section of high-speed swerves, Russell said, which is similar to the fast Jeddah street track in Saudi Arabia.
The drivers' fears about potential crashes were underlined by an fiery accident in Formula 2 practice involving Thai driver Tasanapol Inthraphuvasak, who was uninjured in the incident.
