Mercedes driver Lewis Hamilton had a difficult outing during Friday's practice session at the Monaco Grand Prix, comparing it to the "bumpiest roller-coaster ride ever".
The seven-time world champion was 12th quickest after the second session of the day, more than 1.6 seconds off Charles Leclerc and his Ferrari team-mate Carlos Sainz.
Hamilton criticised the track and said the bumpy ride was difficult to endure, even as home favourite Leclerc completed an impressive practice double with the Ferrari man now favourite to take the all-important pole position on Saturday at Formula One's showpiece event.
Hamilton's revival at Barcelona a week ago could be short-lived following a troubling day in which he was jolted in his bouncing Mercedes.
Mercedes felt they had resolved the majority of the porpoising issues which have so far plagued their season, so Hamilton's frustrations will be a major cause for concern as they bid to get their campaign back on track.
"It is the bumpiest the track has ever been and possibly the bumpiest track I have ever driven," said Hamilton.
"Our car bounces a lot. It is different bouncing to what we have experienced in the past, it is at low speed and the bumps on the track make it worse.
"I am fighting the car. I don't remember experiencing anything like that before. When you do try to put a lap together, the grip doesn't feel terrible, it is just my eyeballs are coming out of their sockets.
"We have work to do overnight to fix that and - as anticipated - we are not as quick as the Ferraris and Red Bulls. Our challenge is to stay ahead of McLaren.
"I really hope for a better day tomorrow. It feels like the car has the potential to be up there but there are all these things that are hindering us at the moment - but we will not stop fighting."
There was nothing new at the top of the speed chart on Friday with Ferrari and Red Bull once again dominating, but the Red Bull camp is settled following team orders that cost Sergio Perez a win in Barcelona.
Red Bull ordered Perez to surrender the lead to teammate Max Verstappen, who won his third consecutive race and fourth overall to take the F1 points lead from Leclerc. Perez found the call “unfair” but said on Friday in Monaco the team had discussed the order.
“We spoke after the race. It’s all clear, and we all agree that we could have done a better job,” Perez said. “We are on the same page and we move on. It’s a great atmosphere at Red Bull and we have great momentum.”
