Please provide a source.
I can't find anything official but to me, even if he's not registered in our playing squad he is still an employee on our books and still takes up a loan slot. It's a rule against the business side of a club, not on the submitted squad list of a club. He's still loaned to us whether we plan to use him or not.
Happy to be proven otherwise but never seen it before and can't see it being allowed.