The 28-year-old, winner of the 2025 Ballon d'Or, has been unwell since Monday and was deemed unfit for the league phase fixture in Spain.
Dembele's absence adds to a recent disrupted run of form in which he has struggled for consistent match fitness.
He missed domestic fixtures against Olympique Lyonnais and Le Havre with a calf injury before returning to action on November 26th in PSG's 5-3 Champions League win over Tottenham Hotspur, when he played 12 minutes as a substitute.
The France international then made further cameo appearances off the bench in a 1-0 defeat by Monaco on November 29th and a 5-0 Ligue 1 victory over Rennes last weekend, clocking close to half an hour in each match.
Against Rennes, Dembele set up Goncalo Ramos in stoppage time, suggesting a gradual return to sharpness before illness struck ahead of Wednesday's European tie.
PSG are second in the 36-team league with 12 points from five games, while Athletic Club sit in 27th place on four points.
