Red Bull's Perez crashes in first Hungarian Grand Prix practice
The Mexican, second overall but a massive 99 points behind dominant teammate and double world champion Max Verstappen after 10 races, brought out red flags when he smacked into the tyre wall at turn five.
"I cannot believe this," said Perez over the team radio, with the stricken car looking like it had suffered some heavy damage.
"I clipped the grass, I think on braking, I just lost it," he added.
The Mexican has failed to qualify in the top 10 in his last five races, only once standing on the podium in the same period, and needs a strong weekend with Red Bull reserve Daniel Ricciardo increasingly in the frame as a possible replacement.
Perez missed the rest of the session, with the car taken back to the pits on a truck for mechanics to start what could be extensive repairs.
"It’s obviously frustrating...hopefully it (the damage) is contained mainly to the front right corner, which hopefully will be repairable in time for the next session," said team boss Christian Horner.
"It was unfortunate, he just put a wheel on the grass and made a mistake into Turn Five.
"Hopefully, he won’t have lost too much through this session because in these conditions people aren’t getting many laps in. But obviously, not an ideal way to start the weekend."
Mercedes' George Russell, who took his first career pole position in Hungary last year, was the fastest overall with his final lap in a time of one minute 38.795 seconds.
Rain began falling during the stoppage and then got stronger.
Australian Oscar Piastri was second on the timesheets for McLaren, with Lance Stroll third for Aston Martin and Lando Norris fourth for McLaren.
Verstappen and Ricciardo were among seven drivers who did not set a time.
Mercedes' seven-time world champion Lewis Hamilton, winner a record eight times in Hungary, was one of the seven. The Briton was out of his car before the end of the session with nothing to gain from being on track in the conditions.
Ferrari's Carlos Sainz also brought out red flags when he beached his car on a kerb at turn three with 14 minutes remaining.
