Robert Kubica has admitted he will be disappointed if he does not complete his Formula One comeback after taking part in another audition for Williams.
The 32-year old Polish driver, who has not started a grand prix for more than seven years following a harrowing rally crash in 2011, managed 108 laps of the Yas Marina circuit in Abu Dhabi as the British team assess their driver options for next year.
Kubica, now managed by former champion Nico Rosberg, will return to the car at the same venue on Wednesday and is the front-running candidate to replace Felipe Massa in 2018.
Tuesday's test marked Kubica's third outing for Williams - following trials at Silverstone and the Hungaroring - and his sixth of the year after he also tested for Renault.
The French team however, had reservations over Kubica's fitness, particularly the right arm which he nearly had amputated following his life-threatening crash - and opted to sign Carlos Sainz instead.
But Kubica, a one-time grand prix winner and considered one of the finest performers of his generation, has claimed he is in better shape now than when he last competed at the 2010 season-ending Abu Dhabi Grand Prix.
"It has not been easy, but I am in far better physical shape than when I was racing in 2010," Kubica said. "The motivation is there and the body is reacting in a good way.
"I am starting from scratch because Formula One has changed so much over the past seven years, but the experience I gained while racing in F1 has helped me to get on top of the learning process.
"I have some limitations and I have to adapt, but one positive thing is how my body is reacting and how natural I feel every day when I am driving these cars, so that gives me a lot of confidence.
"What the future will bring, I do not know, but today was the kind of day that if nothing else happens there will be disappointment because I feel confident and comfortable."
Russian Sergey Sirotkin is sharing the testing duties with Kubica in Abu Dhabi. Canadian teenager Lance Stroll is already confirmed for 2018 but Massa's retirement leaves a vacancy at Williams.
Daniil Kvyat, Pascal Wehrlein, Britain's Paul di Resta and Sirotkin are all potential candidates, but it is Kubica who leads the way to complete what would be considered as one of sport's most remarkable comebacks.
"There are lot of people wishing to see me back because of the story, but there is no discount for the story," Kubica added. "I have to make sure if I get the chance I am ready and prepared.
"If I do come back I am not here to make up the numbers. I have to make sure I can provide the best of Robert Kubica."
Williams, who finished a distant fifth in this year's constructors' championship, are set to confirm their driver line-up for 2018 before the New Year.