Kevin Magnussen says Haas has not solved the problem that affected the American team so badly in Bahrain.
The outfit looked to have started 2019 with a car that was 'best of the rest', but Haas' race pace plummeted during the race a fortnight ago in Bahrain.
The team brought a new rear wing to China to address the problem, but Magnussen told the Danish newspaper BT that it is not the answer.
"It's still a problem," he said.
"We still have difficulty getting the tyres up to the right temperature, and I think it's the same problem we had in Bahrain. We need to understand why and how we can improve," Magnussen added.
He said the "window" of optimal tyre performance for Haas is "very small".
"It's really strange that we can be really good one weekend and really bad the next. We honestly don't understand it, but we think it's related to temperature," said Magnussen.
As for the race, Magnussen therefore lamented in Shanghai: "It's colder here than in Bahrain, so the problem can be even bigger."