Yeah Zhang seems like a very dangerous opponent for someone like Wilder - he's big heavy and comes forward, it reminds me of Wilder v Ortiz, where Wilder only just managed to get himself out of there with KO, up until that point he got very badly roughed up.
And he was saved by the doctor in their first fight.
Zhang is a big old southpaw that seems to have power in what appears to be arm punches. If Wilder can avoid those he may be OK but if fighters like Molina can put him onto Queer street, I can't see why Zhang can't spark him out.
Zhang needs to come in a bit lighter though. He looked gassed before the mid rounds by Parker but Parker moves a lot more than someone like Wilder. Quite an intriguing fight really