The Pole, who suffered life-threatening injuries in a rally crash in 2011, was beaten to a race seat at Williams by Sergey Sirotkin.

He took on a reserve driver role, which involves driving at pre-season testing, in-season testing and three free practice sessions.

After completing 48 laps in the car on Tuesday at Barcelona, Kubica grew frustrated with a line of questioning, saying he had not made changes to the car to help any limitations.

"If I keep changing things you will keep saying I have limitations. We should stop talking about this," he said.

"If I can jump in the car and do the job, I think that's fair enough. Of course I have my limitations but I never hide them.

"The problem is I was too honest with everybody and they kept asking questions, I think we should stop it.

"I have been always comfortable, it was only media talks that I was not comfortable."

Kubica called for critics to stop talking about any potential shortcomings and instead focus on the positives he could deliver in his reserve role.

"We have things to concentrate on," he said. "I'm living a good experience, I'm enjoying my role.

"I'm happy to give positive messages, not always the same story after many years."

Kubica, who finished seventh fastest overall, was pleased to get back in the car but admitted the cold conditions made it difficult to get a read on performance.

"It was all OK, difficult conditions and a difficult afternoon," he said. The conditions are extreme so for sure they are not helping us.

"We did some evaluation work. It was good to be in the car, good to have a feeling in the new car.

"It will give me a better idea for our engineering department which area we need to improve.

"There are some very positive things about this car but some things we have to get on top of, which is normal with a new car which has quite different approach compared to last year."