Robert Kubica says he will stay off the curbs this weekend in Bahrain because Williams does not have enough spare parts.

"We cannot afford to break anything," said the Pole.

Kubica has had a tough return to F1 after eight years, with the highly uncompetitive Williams car, a mistake-strewn season opener in Australia, and Jacques Villeneuve saying disabled people do not belong on the grid.

Now, he says Williams is lacking spare parts to repair any damage in Bahrain.

"We are not competitive and now there is this added factor, which makes life only more complicated," said Kubica.

"We just need a little more time."

Kubica's teammate George Russell added: "We see light at the end of the tunnel, but it is a rather long tunnel."