Sanader was arrested near Salzburg on 10 December and the following day was placed in 14-day extradition detention.
By 27 December Sanader can express his position whether he will accede to his transfer to Croatia where he is wanted in connection with a corruption investigation. He has not yet expressed his opinion on the matter.
On Thursday, Austrian federal prosecutors interviewed the former Croatian premier as part of a money laundering investigation which was launched after a Tyrolean bank reported a case implicating Sanader and some other suspects.
In case Austria issues an indictment against Sanader in the money laundering case, the proceedings will make his extradition to Croatia more complicated because Austria would like to close the case before handing him over to Croatia.
According to the Austrian APA news agency, the extension of Sanader's custody is likely.
In the event that Sanader accedes to his extradition, he might be transferred to Croatia in two or three weeks' time.
If he refuses extradition, the court in Salzburg will decide on the matter and Sanader may appeal to a higher court against the trial court ruling on his transfer back to Croatia, which may substantially delay the extradition process.