Haris Vuckic will not play for Newcastle again this season through a knee injury, according to Slovenia Under-21 coach Tomaz Kavcic.
The 19-year-old was recalled to the first-team squad last month to provide cover for injuries following a loan spell at Championship side Cardiff.
However, the midfielder has now been added to manager Alan Pardew's injury list.
"I can confirm that Vukic 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."