Baku F1 practice drain cover damage unacceptable - Valtteri Bottas

Bottas was returning to the garage after his installation lap at the beginning of the final practice session for F1's first race at the new Baku city circuit when his Williams traversed a loose grill on the track.

Debris was seen flying into the air from the impact, close to some marshals that were standing on the pitwall.

Bottas had to sit out the rest of the session while Williams repaired bodywork and radiator damage and examined the car's gearbox.

"It's not acceptable at all that these kind of things still happen," said Bottas.

"It's not the first drain cover in F1 that has come loose, and luckily it was in the pitlane.

"I felt it when I was on it and it hit the car. Seeing the replay, I think the marshals were quite lucky."

This latest incident comes after a drain cover worked loose during practice for May's Monaco Grand Prix, puncturing a tyre on Nico Rosberg's Mercedes and also damaging Jenson Button's McLaren-Honda.

Williams performance chief Rob Smedley put the Bottas incident down to a "shitty set of circumstances" but urged the organisers, the FIA and the teams to collaborate more closely to improve circuit safety.

"I don't know whether there's something fundamental going on or whether it's just a bad set of circumstances that we're going through and coincidences," he said.

"Charlie Whiting and his people from the FIA are pretty relentless in their quest for making the track safer, for getting rid of any stupidity in terms of layouts or anything like that.

"All we can do is be thankful nobody got hurt - either the driver or the marshals, who had quite a near miss with the drain cover that flew off and went towards them, and second of all try and learn from it.

"The promoter, the FIA, and the teams themselves should see if there's a better way of working to avoid these things."