Controversy flared in the second half of FC Porto v Manchester City (0-2). Marc Guéhi caught Gabri Veiga in the face with an elbow and escaped punishment, drawing criticism towards VAR Pol van Boekel.
The Manchester City defender struck the FC Porto player in the face with his arm during a duel. Referee Szymon Marciniak did not penalise the incident, and Van Boekel did not send him to the pitchside monitor to review it either.
Shaken by the collision, Veiga had to go off for treatment. The Spanish midfielder, in Portuguese service, did not need to be substituted, however.
On the touchline, Porto coach Francesco Farioli threw his hands in the air as he questioned why Guéhi had not been punished by the officials. Home players and supporters were furious too.
Van Boekel also came in for criticism last weekend. Working as VAR, he did not call referee Sander van der Eijk over to the screen after Ruben van Bommel's challenge on Aaron Bouwman.
On Monday, Mike Verweij of De Telegraaf reported that Van Boekel is heading towards retirement. "I think the intention is for him to stop in December or January. There is some discussion about whether they should continue with him or not. But then you must not make too many decisions like this, or actually forget to make them," was the line on Kick-Off.