I think it's difficult and a good point made about refs not liking players or basically respecting them. I think at surface level Klopp won't mind too much who is captain, he expects everyone to lead, however as it's the captain who is in the refs ear then the choice is an important one. It's easier to rule out players that it is rule them in. Mo gets no respect from refs, his English is okay but he's not that kind of personality to argue something, he's more arms than mouth. Robbo isn't high up on respect either as evidence shows with the the response to his altercation with the linesman, he was painted as the villain by pundits, ex refs etc so despite being vocal and I'd like a Scot to wear the armband I think there's already an agenda round him.
It probably is Virgil as his English is good enough, he's more imposing than other figures. I also believe referee's treat foreigners differently especially if you aren't white so that also limits the options. (Let's be honest that's why Salah never gets a foul)
