Robert Kubica will definitely be out of action for the first quarter of this season's 20-race calendar.
Earlier, medical specialists had predicted a one-year recovery from the Pole's multiple rally crash injuries, cautioning that athletes often heal much faster.
"At the moment it's hard to predict," answered Renault team boss Eric Boullier when asked about 26-year-old Kubica's expected recovery time by Auto Motor und Sport.
"He's not coming back for the next three months. But to say six months or more would be purely speculative," he added.
Boullier said Kubica has been making "surprisingly rapid progress" this week, can move the fingers on his injured right hand and will be under the knife for a further five hours on Friday for work on his elbow and shoulder.
"He was asking about GP2 and Formula One and joking as usual," said Boullier, recalling his most recent visit with the Pole.
"He wants to know the results of the tests, so we will give him all the data of Jerez on Monday."
Boullier admits Kubica's convalescence is a "heavy blow" to Renault, but he vowed not to bow to pressure and prevent the team's drivers from participating in dangerous extra-curricular hobbies from now on.
"No, we are not changing," said the Frenchman. "Robert is a racer, I'm a racer. If we had banned rally driving and karting, he would not have been happy.
"The driver is the most useful when they feel comfortable with the team. Absolutely. Up until the corner where he had his crash, Robert was a happy man," added Boullier.