Robert Kubica says he understands why question marks remain over his ability and admits he would also have doubts about his return to Formula 1 if he was a team boss. 

The 35-year-old Pole will complete a remarkable comeback to F1 with Williams in 2019, eight years after suffering severe injuries to his right arm that cut-short his promising career in the sport. 

Kubica, who tested for Renault and Williams throughout 2017 and 2018, said he has come to accept why people had struggled to believe a return to grand prix racing was realistic, having been absent from the F1 grid since taking part in the 2010 Abu Dhabi Grand Prix. 

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"If I would be a team principal I would also have doubts," Kubica said.

"This year has been very useful because at the first meeting, I remember, I said 'If you have any doubt, we shouldn't be doing it, because in difficult times it's easy to point the finger on my arm - I want to make sure that you are sure that I can do it'.

"First of all I have to be sure that I can do it, that's why I'm here, but second of all the team has to be convinced that I'm able to do a job."

The 2008 Canadian Grand Prix winner believes his comeback shows everybody, including those that did not believe a return was feasible, that “nothing is impossible”. 

"If I think I will not be able to drive competitively fast I would not be here," he explained. 

"This is a normal way of thinking, that people see my limitations and they ask how it's possible that I do it.

"I know that it's hard to believe but Williams has seen it this year and I have seen it [for] the last 16 or 18 months, since I first tested an [older Renault] F1 car in Valencia that I can do it.”

Deputy team principal Claire Williams praised Kubica’s determination to return to F1 on a full-time basis and is confident he will help the British squad - which slipped to the bottom of the constructors’ championship in 2018 - turn around its fortunes next season. 

“He has an amazing spirit and a fantastically tenacious personality and hugely passionate about Formula 1 and his traits combined make him a driver we’re really looking forward to working with next year,” Williams said. 

“That talent that we know Robert has means we’re really excited that he is going to be bringing that to Williams next year. 

“His intelligence in the cockpit and his engineering ability we believe is really going to help us drive this team forward as we start a new chapter for this team in 2019.”