Several people I know felt that this use of “concern” was correct: “She felt concern, but not enough to sacrifice...” I felt that it should be “concerned”. Two of them are professional writers, so I can’t argue much, but if “concern” is also correct, what is its function? Noun or adjective? If it’s a noun, shouldn’t it be “a concern”? If it’s an adjective, shouldn’t it be “concerned”? In dictionaries, “concern” is either a noun or a verb, not an adjective.
Oddly enough, the same people felt that “She felt scare” was clearly wrong. If “scare” is wrong and “scared” is correct, then shouldn’t the same hold true for “concern” and “concerned”?
On the web, I do see many people using “feel concern” although it is slightly less common than “feel concerned”.