"The scenes depicted in the images are clearly contrary to the values of respect and tolerance UEFA works hard to promote," European football's governing body said in a statement on Wednesday.
The images, plastered on wallpaper on the walls of the Alvalade stadium's tunnel leading to the pitch, show a group of aggressive-looking, masked fans clashing with stadium stewards. One of the fans is pictured burning a flare, an illegal object to bring inside stadiums in Portugal.
"UEFA has a zero-tolerance approach to violence and these images show at the very least an ambivalent position towards fan trouble and fan violence," UEFA said, explaining its decision to request that the club remove or cover the images for UEFA matches.
Sporting did not comment on UEFA's request, but had previously said the pictures were not disrespectful and accused local media of having singled them out from a wider range of images.
"The images in the corridors around the locker rooms are part of management's decision to show respect for the history of the club and its fans," Sporting said after Portuguese newspaper Publico showed the photos last week.
The club added that UEFA and the Portuguese League had not only approved of the wallpaper images but also praised them.
Sporting, UEFA Cup runners-up in 2005, are considered one of the 'big three' clubs in Portugal together with Porto and Lisbon rivals Benfica.
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