Max Verstappen was caught by surprise as he crashed with Lance Stroll during an action-packed FP2 at the Portuguese Grand Prix on Friday.
The pair collided at turn one during the second session of the day, with Stroll turning into the corner and cutting off the space for Verstappen, who had not quite been able to get past the Racing Point on the main straight.
The incident brought out the red flag for the second time in FP2 – the first occurred after Pierre Gasly's AlphaTauri caught fire – and the duo were summoned by the race stewards.
"I was so surprised. He just turned in. I was coming up to him. I don't know where I have to go, I was starting my lap and he had just finished his lap... so we'll see what happens," Verstappen told Sky Sports.
"It's practice two and it's just a shame that we touched and it was just very unnecessary. It's just silly."
Red Bull team principal Christian Horner felt Verstappen and Stroll deserved an equal share of the blame for the incident.
"You've got to go back to the previous lap. Lance has got to that last corner, Max has let him go because he wants to take a tow and he's assuming that Lance was finishing a lap. So he let him past, tucked up behind him, taking the advantage of the tow, assuming he's going to back out because he knows he's there and [Max] is up the inside," said Horner.
"Obviously Lance for whatever reason hasn't seen him, has committed to the corner and turned in. Both of them were expecting the other to back off.
"But if that were a race, Max would have been deemed to be up the inside so therefore the car on the outside should have given way.
"If I'm absolutely honest, you can look at it and say both had a role to play. Max has assumed Lance was going to back out, while Lance may not have even been aware Max was there.
"Both sides are going to argue their case but you probably have to say it's a 50-50 and that's it."
Valtteri Bottas recorded the quickest time in both free practice sessions in Portimao with his lap of one minute, 17.940 seconds on soft tyres in FP2 the best of the day.
Verstappen was second quickest in that session despite his crash, and although he was 0.595s slower he registered that time on the hard compound.
Championship leader Lewis Hamilton slipped from second in FP1 to eighth in FP2, having been frustrated by the balance of his Mercedes in the second session.