Luka Jovic -- a star striker for Real Madrid -- broke quarantine last week in order to see his model girlfriend ... and now, officials say he's facing jail time for the reckless move.

Jovic, along with the rest of his teammates, were advised to stay in two-week isolation earlier this month after a Real Madrid basketball player tested positive for coronavirus.

But, Jovic reportedly broke quarantine in order to fly back home to Serbia to see his pregnant girlfriend, Sofija Milosevic, last Thursday ... and now, authorities in his homeland are PISSED that he didn't isolate properly.