Gnabry tests positive for coronavirus
Bayern manager Hansi Flick confirmed that Gnabry would likely be absent from the game at the Allianz Arena after complaining of a sore throat.
Bayern later announced the 25 year-old had tested positive for COVID-19.
The defending champion was already missing star striker Robert Lewandowski due to a knee injury, leaving it without an attacking duo who have been directly involved in 63 goals in all competitions this season.
PSG, meanwhile, had already confirmed Marco Verratti and Alessandro Florenzi would miss the first leg after returning positive coronavirus tests.
Bayern defeated the Parisians 1-0 in last season's Champions League final, with Kingsley Coman scoring the winner.
Should it avoid defeat in the first leg, Bayern would become only the second team in the competition's history to go 20 consecutive games unbeaten, after Manchester United (25 between 2007 and 2009).
However, Bayern has only won four and lost five of the previous 10 meetings in this tournament with the Ligue 1 champion. Only Real Madrid (10) has beaten Bayern more often in the competition.
