Responding to a letter dated October 8, Zhang said Hammam was trying to "intimidate and create technical legal issues and objections in the hope that the more serious allegations of secret commissions, bribery, corruption and other wrongdoings are never exposed to the light of day."
The AFC, which Bin Hammam headed for nearly 10 years, provisionally suspended him for 30 days on July 16 and then invoked a clause which allows them to extend the ban by 20 days.
Zhang wrote to the AFC's member associations to deny any "conflict of interest in the ongoing AFC Disciplinary Committee action against Bin Hammam" or that he had "personally benefited from his support".
He also denied interfering with the ongoing disciplinary action against Bin Hammam, who was "being dealt with as provided for under the AFC Statutes and the AFC disciplinary code".
FIFA banned Bin Hammam for life for bribery during his failed bid to become president of football's world governing body last year.
The Court of Arbitration for Sport (CAS) overturned that ruling but FIFA suspended him for 90 days after CAS said their decision was not "an affirmative finding of innocence".
Bin Hammam has denied the charges levelled by the AFC and FIFA.
