The Bhoys midfielder is currently suffering from a hamstring problem and has not trained on Wednesday.
Celtic boss Brendan Rodgers has confirmed that Brown could be struggling to get fit ahead of the game.
The Scottish Champions will be without Felipe Benkovic and Tom Rogic as well.
Rodgers also added that Brown may not be risked this weekend against St Johnstone, and that he could return after the international break.
“We’ll need to have a look at Broony”, Rodgers said in the Scottish Sun. “He could be struggling. He didn’t train this morning [Wednesday].”
Brown is a key player for Celtic and his absence is a major blow. He is the lynchpin of the Celtic side and the fans will be hoping that he returns to full fitness at the earliest.
The Salzburg clash is undoubtedly Celtic’s toughest test in the Europa League. Celtic will be looking to get a positive result tonight to consolidate their position in the group.
However, one piece of good news for the Celtic fans is that Odsonne Edouard should be available for selection.