Robert Kubica says that a lack of grip saw him struggle throughout the 71 laps of the Austrian Grand Prix on Sunday.
The Pole crossed the line last of the runners and was almost a lap behind teammate George Russell.
Kubica affirmed that the hot temperatures in Spielberg on Sunday didn't help his cause and that he was even sliding through some high-speed corners.
"It's difficult to comment when you finish three laps down and nearly a lap down on your teammate," he said. "The comments are the same as always. I'm sliding, I put too much stress in the tyres, I have no grip.
"Even if I try to keep up with the pace I can do it for two or three laps but then the tyres are overheating. I was even sliding at the exit of Turn 7 which is a fifth/sixth gear corner.
"It's difficult to extract anything if you are just sliding and degrading. Whenever you put more slip into the tyres you go slower. I have to drive to not slip them but then the pace is very slow.
"I try everything, it's not the first time I'm not trying. It's just I'm lacking overall grip. In this condition when it's very hot, there's overheating and tyres are suffering a lot."
Kubica added that it was "too early" to talk about his future position at the Grove team, but says "why not" over his place for 2019.
Bahrain International Circuit - Winter testing