Pirelli's Mario Isola has fended off Haas' complaint about the difficult 2019 tyres.
Haas has an objectively fast car this year, but the American team is struggling more than any other rival to get temperature into the tyres in the race.
Team boss Gunther Steiner has said the situation is "not Formula 1".
But Pirelli F1 boss Mario Isola distanced the Italian tyre supplier from Haas' issues.
"I find it difficult to judge, because it is related to their chassis," he is quoted by Russia's Championat.
"It seems that in qualifying they are fast, but in the race the temperature of the tyres drops and they cannot maintain the same speed.
"They need to find a way to load the rubber more strongly, as they were designed to work most effectively at high temperatures," Isola said.