Professional wrestling is a profitable entertainment venture in Great Britain, Germany, France, Italy and Spain. Japan, as well. Slightly different style, but a similar show. Not Olympic style wrestling. The WWE has had success promoting themselves in England and Germany.
If there are people in those nations with income to spend on that kind of entertainment do you think the NFL couldn’t capture some of it? NFL teams would play about a third the number of games their soccer teams do. It would be a spectacle. NFL in the US competes with countless college games and the loyalty to those teams. In Europe the NFL would be the only American football to see. (there are low level leagues in some countries). And Europeans do watch TV. A bonafide effort to establish actual NFL in Europe is not an if, but a when.
The other obvious country is Canada. While they protect their CFL by prohibiting NFL entry, many of those franchises struggle financially. Toronto averages 15,000 fans per home game. Vancouver 26,000. Montreal 21,000. The NFL is already popular in Canada. Some wealthy, enterprising, and politically dialed in Canadians will get it done at some point.