No, that's not a correct use of shall.
Shall is used to describe future plans, intentions, or instructions. For example, General Douglas MacArthur said
We shall land at Inchon
to express his determination to land on Inchon island in Korea.
But in your example, you're not using it to describe a future plan or intention, you're describing a set of options.
You might be thinking of the word should; you could phrase your sentence like
...should their enemy be England or Croatia.
But that's not really correct either, because should means something like "if". If I read this sentence, I would think "The team will win if the enemy is England or Croatia, but not if it's any other country."
A slightly formal but correct phrasing for what you are trying to say might be
...whether their enemy be England or Croatia.
This is an example of the subjunctive, which is why be is used.
A more informal way to put it would be
...whether their enemy is England or Croatia.