In English sports, we have a long-standing tradition of saying ARE. You may be correct that both are OK, but I believe that technically, "IS" is correct because you are referring to a single entity (e.g. the club/team).
You wouldn't say Zinchenko ARE signing for Arsenal, because he's a person, i.e. a single entity and it shouldn't be any different when referring to a single entity that reflects a collection of people.
Or maybe it's just a US v English thing, as per the following example.
Perhaps you’ve had this experience: you’re talking with a friend about your family, and they ask something general. But when you reply with a quick description, are you referring to one family, or are you talking about several individuals? The need for subject-verb agreement will help determine...
strategiesforparents.com
Both “My family is” and “My family are” are correct in British English, while “My family is” is most common in American English. This is because “family” is a collective noun, and American English generally treats collective nouns as singular, while British English treats them as plural.