Boss Eric Boullier recently imposed a mid-October deadline for the Pole, who is under contract only to the end of 2011, to say whether he will definitely recover from horror injuries sustained in a February rally crash.
He has agreed to extend that deadline a little further, but Kubica's doctor this week admitted that the 26-year-old is still "a few months" from the end of his rehabilitation.
"Our goal is to get him back in F1," Dr Riccardo Ceccarelli told Tuscan television Lucca.
"But he will still need a few more months of rehabilitation. The cuts were so bad that many colleagues and specialists had ruled out a return to the wheel for Robert.
"But, clinically, little by little everything has improved and the hope to see him driving as soon as 2012 is becoming more and more concrete."