The Renault driver had been tipped as a possible title challenger this year before he suffered life-threatening multiple injuries in a crash at the Ronde di Andora Rally in February.
His senior doctor Riccardo Ceccarelli, who is in charge of Kubica's rehabilitation, said this week that he will need another operation on his right elbow before he can move into a more intensive period of rehabilitation work.
He said: "We need to do this to free his elbow more. With his elbow blocked, we haven't had the chance to work on a full recovery programme as we would do normally.
"However, we have kept the other joints moving as much as possible, with the goal of having as much flexibility as we can - the greatest possible muscular mass available once the elbow is unblocked."
Kubica's future as a racing driver depends on the success of this next operation and his ability to recover and attempt to make a return to the cockpit.
He was replaced at Renault this year by experienced German Nick Heidfeld, 34, a veteran of 183 Grands Prix, but since grabbing third place in Malaysia in April, he has been unable to shine.
Russian Vitaly Petrov, in his second season, has improved steadily but the team has lacked the sheer pace and leadership of Kubica - and would welcome him back, fully fit, as soon as possible.
Realistically, however, that is unlikely to be any earlier than next year as Kubica, 26, works to ensure his recovery is complete.
Kubica to undergo another surgery on road to recovery
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