Robert Kubica has made it clear he would be "disappointed" not to earn another chance to race in Formula 1 after brushing off ongoing questions about his abilities, claiming he is physically in the "best shape" of his career.

The Polish driver is completing further tests with Williams, completing 100 laps behind the wheel of the 2017 car for the first time on Tuesday in Abu Dhabi, as he looks to claim the seat left by Felipe Massa for next year.

The main area of debate surrounding the former Grand Prix winner's attempted comeback has been whether the weakness in his right arm, caused by severe injuries sustained in the rally crash which ended his first stint in F1 six years ago, is too much for him to overcome.

"For sure I have some limitations but in some way my body used some compensations, which is not wrong, we are human beings and our brains are used to help our bodies overcome disabilities," he said after driving on Tuesday.

"This is something I think I’m on top of. Psychically I think I have done a great work, good work in the last six months. It hasn’t been easy, it was not like I have been lying in my bed, actually, I'm probably in physically my best shape and by far a better shape than I was when I was racing in 2010."

Considering his level of performance, Kubica feels he is improving each time he climbs inside the cockpit, having made a return with Renault earlier in the year, and is very happy with how he feels physically behind the wheel.

"I’m having the same approach for the last six months. I’m taking my opportunities, my days, behind F1, as a step-by-step, as a day-by-day," he explained. "I try to learn as much as I can, give the best job, the best service I can provide and try to learn myself.

"Of course it’s not exactly the same as it was seven years ago, I have some limitations, I have to adapt myself also, I have to learn my body, but one very positive thing is how my body is reacting and how more natural I feel every day when I’m driving an F1 car. It’s giving me a lot of confidence."

That confidence is also making the 32-year-old more determined to achieve his ultimate goal of racing in F1, admitting not doing so would be tough to take after coming so far.

"In the end what the future will bring I don’t know but definitively if you look at the overall picture, where I was 12 months ago and where I am now, it has been a good 12 months," he said.

"For sure today was the kind of day that if nothing more happens, there will be some disappointment because I feel very confident and very comfortable, but also if you think where I was, I can only be happy and a bit proud of what I achieved in the last 10 months."