Consider, perhaps, that ‘a subject’ can be a slave without being ‘a citizen’.
Consider that a 'subject' cannot become a monarch, thus tha issue didn't exist in common law.
Well if we are going to continue this.
I haven't really thought about it but I suspect that if we looked at the common law question, we would find that there wasn't anybody who was a citizen and not a subject.
The concept of "citizenship" dates back to Roman law where there was a clear distinction between Roman citizens and others. After 476, I don't think you had much of that in Western Europe or England.
You had whatever rights the king said you had and he could (at least until Magna Charta), cut you off without cause or notice.
Subjects, depending on who they were, probably had rights against slaves or lower level subjects for that matter; but they were still subjects of the state.