Robert Kubica believes he is capable of a full-time comeback to Formula 1 with Williams next year.
The Pole has not raced in F1 for seven years after suffering life-changing injuries in a rally accident in 2011.
The 32-year-old tested for Williams in Abu Dhabi last week and is driving in the team's simulator this week before a final decision is made.
"The most important thing is the confidence is there and the belief I can do it is there," he told BBC Sport.
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The former BMW Sauber and Renault driver is one of several contenders for the final available seat on the grid, partnering Canadian Lance Stroll.
Other drivers in the frame include Renault reserve Sergey Sirotkin, ex-Sauber driver Pascal Wehrlein, former Red Bull driver Daniil Kvyat and Williams reserve Paul di Resta.
Kubica, who has only partial movement in his right arm as a result of the injuries he sustained, has tested three times apiece for Renault and Williams this year as he seeks to make a comeback to F1.
Asked if he felt he was 100% ready to make a return, he said: "100%? It depends. I have never been ready 100% even when I have been racing on my, let's say, gold times.
"I have done a lot. I have proved myself a lot and there are a lot of things which give me a lot of confidence and give me positive answers but the decision is not on my side.
"Whatever the outcome will be, of course when you are next to it it would be nice but you never know, I want to live day by day. I still keep training, I still keep preparing as [if] I would have a chance."
He admitted he still needed time to adapt to certain aspects of F1 after so long away.
This is believed to be a reference to the particular characteristics of the Pirelli tyres, which are notoriously difficult to handle - this was something even seven-time world champion Michael Schumacher struggled with when he returned to F1 after three years away.
"There are things which require time because the last time I drove an F1 car was more than six years ago and F1 has changed a lot and you have to get knowledge about things to extract maximum from the car and I have learned a lot from my side and my confidence has gone up," Kubica said.
But he said he would not be trying to make a comeback if he did not feel he could perform at a high level.
"I cannot be 100% sure because I think no-one is 100% sure," he said. "But I can have confidence and what I was looking for was to get a feeling and belief I can do it and that's the most important.
"The situation is not easy with my limitations but I think honestly there were a lot of questions of mine about my limitations and fitness and we should agree in the end - because I have shown - although I have limitations, fitness-wise I am ready and in fact I have never been in such a good shape as I am now.
"Of course I have to work harder because I have my limitations, and I have to prepare better and in a different way my body and mental strength, but that is part of my life."
Williams are still in a quandary over their final decision, partly because the circumstances of the Abu Dhabi test make it difficult to be absolutely clear about performance there.
Aspects of Kubica's performances were encouraging, sources close to the situation say, including his race pace, but Sirotkin appeared quicker in terms of ultimate pace over one lap and the Russian's strong showing surprised and impressed the team.
Sirotkin will also visit the Williams factory this week as both he and Kubica complete what the team describe as "post-test reviews".
Of the drivers on their list, Sirotkin is said to have the most financial backing but Williams said this was not the main factor in their decision. Their priority is on-track performance.