Williams may struggle simply to qualify for the 2019 season opener in Australia.
France's Auto Hebdo said George Russell and Robert Kubica are precariously close to the 107 per cent qualifying cut-off rule.
When asked about that, rookie Russell said: "I drive the car, I don't have a calculator with me.
"Obviously, it is not the best. We are a long way behind."
Pole Kubica, on his feted return to F1 after an eight year absence, revealed that he was told to "stay off the kerbs" in practice due to a lack of spare parts.
"Unfortunately we don't have many spare parts but we are making the most of what we have. The car is very difficult to handle," he said.
Kubica acknowledged that Williams is alone, right at the back of the field.
"We do not have much to fight with," he said. "I will try to do my job the best I can, but it is not easy.
"The feeling was better in Barcelona. It's difficult to draw conclusions because we have problems," Kubica added.
