Originally, Ferrari had an option with Robert Kubica for the Polish driver to join the Italian team in 2013. This was signed in the summer of 2010 and was renewable each year. From what I understand, Ferrari let the option lapse in July this year, at a time when Robert was still recovering from the injuries that he suffered in a rallying accident in February. He remained under contract with Lotus Renault GP until the end of this year. That deal comes to an end in December and while the team may feel a moral obligation to provide the Polish driver with a car in order to ascertain whether or not he is fit to return to racing, there is no commitment beyond that.
In any case, the signs are that either Kubica is not going to be ready to return in time for a Renault test this winter; or that he does not want to race for Lotus Renault GP and would prefer to try to get a job somewhere else. It is logical that Ferrari would retain at least some interest in him given how keen the team was to sign up previously, but there need to be tests, not just to ascertain whether he is still able to compete, but also to help him build up his physical strength, which is an essential part of the recovery process. This is not easy given that there are testing restrictions. Having said that if Kubica is still able to drive as he used to be able to drive, Ferrari is the perfect choice as the Italian team can have him running around at Mugello and Fiorano in a two-year old car every week if it chooses to do so.
All this is theoretical until we discover whether Robert is able to drive F1 cars as he used to, or not. There seem to be different stories coming out of his camp: some saying that he is fine and all is well; and others saying that there is much more recovery needed. The Renault situation is fast becoming irrelevant as unless Robert can show he is strong and ready (and that he wants to continue with the team) the logical thing to do is not to wait, but rather decide between the available talent. There are at least three drivers to choose from at the moment: Vitaly Petrov, Bruno Senna and Romain Grosjean all being in the hunt. Grosjean seems to be the man on the up, while Senna needs a solid result after a series of disappointing showings. The team also has the option of looking at others, such as Adrian Sutil or Timo Glock, who are either under contract but have get-out clauses, or are simply available.