Pierre Gasly says he expects to have "nightmares" about Alex Albon's rear-wing after being stuck behind the Williams in the Belgian Grand Prix.
The Alpine driver started from P12 on the grid at Spa and made up a couple of positions after a good launch, but struggled on a planned one-stop strategy with tyre degradation high.
He eventually became stuck behind Albon's Williams machine after a slow pit-stop, with the straight-line speed of the FW45 a well-known strength.
"I lost some time in the pitstop [which] lost the position to Alex," he explained to media including RacingNews365.
"I'll probably have nightmares of that Williams rear-wing because these guys, it seems like a different category on the straights.
"We sort of bet everything on our top speed this weekend, went really low downforce and it was strong all weekend, but I don't know why I was that slow on the straights."
Gasly eventually squeezed by Albon and homed in on a points position, but fell 2.8s short of former teammate Yuki Tsunoda at the flag to claim 11th, to go with his third place in the Sprint on Saturday.
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Gasly's race was also hamstrung by getting caught behind Oscar Piastri on the first lap after the McLaren's contact with Carlos Sainz at Turn 1.
"I had a very good start, made two positions and I was on the inside line which I thought was going to be amazing," Gasly said.
"Until I saw Oscar like 150kph slower than everyone else and I was just stuck behind.
"So I slammed the brake and I just waited for a gap to pass him, but it was just a train passing by it was very painful to watch one-by-one.
"All the guys passing me in from I think ninth or 10th, I ended up 17th so not the start we hoped."