The Slovenian international midfielder suffered the injury playing for the club's reserve side on Monday against Aston Villa.
He has now confirmed that he has suffered 'cruciate ligament' damage.
"I immediately knew that something is very wrong and I suspected that it could be cruciate ligament and the medical examination proved that," he told Ekipa.
"Now I have to wait for the swelling in the knee to go away. Than I will have surgery and four to six months of rest.
"It is very difficult, especially mentally. But I know, that I will be okay, I know that doctors will take care of me, but it will require time and a lot of patience.
Although hugely disappointed, Vuckic is adamant he will return stronger.
"I'm very sad," he said. "I was very close to the first team, I was getting a chance in Europa League and after long time I felt really great. But injuries are part of sport and football. I could feel sorry for myself, that would be easier, but I won't. I'm not like that so I will do everything in my power to come back even stronger."