Vuckic has just returned to Newcastle after his loan at Cardiff City.
"I can confirm that Vuckic is out for the season - he injured his knee," said Kavcic, who is preparing his squad to face Mata Under-21s next month.
"What can we do? Nothing, we will have to find a replacement for him. But of course it won't be easy, he is a great player and a leader of our team."