Socceroos keeper Danny Vukovic was beaten three times in a surprise Europa League defeat while Tom Rogic was absent with a minor injury for Celtic overnight.
Vukovic was between the sticks as Genk went down 3-1 to Norwegian outfit Sarpsborg 08 away from home.
The Australian was first beaten by a clever Patrick Mortensen flick, before Genk levelled after half-time through Leandro Trossard.
In the 54th minute, Vukovic was unable to clear a corner, leading to Kristoffer Zachariassen firing home from close range and Mortensen added another with a bullet.
Elsewhere, Celtic lost 3-1 at Red Bull Salzburg with Rogic not travelling due to an undisclosed injury.
Celtic boss Brendan Rodgers said: “Tom Rogic hasn’t travelled so he’ll be unfit for the game but should be ready for the weekend.”
Apostolos Giannou provided an assist as AEK Larnaca lost 4-2 at Bayer Leverkusen, while Alex Gersbach put in a full shift in Rosenborg's 3-1 home loss to RB Leipzig.
In Saudi Arabia's Pro League, Mat Jurman played a full game as Al Ittihad lost 2-0 at Al Fateh.