Model Ivana Knoll -- who's known as the "World Cup's Hottest Fan" -- posed for pics in a revealing red and white dress while in attendance for the Croatia vs. Canada matchup on Sunday ... with her shoulders and knees fully exposed.

Of course, Qatar takes a modest approach to clothing ... and anyone who visits is strongly encouraged to follow the guidelines.

In fact, the country's tourism page specifically states both men and women are "expected to show respect for local culture by avoiding excessively revealing clothing in public."

Safe to say Knoll's wardrobe choice was a big no-no in the eyes of the locals ... but it doesn't appear she was kicked out of the game or got in any sort of trouble.

As for the contest ... Knoll's beloved Croatian squad ended up easily defeating Canada, 4-1.