"We're bound by pretty tight employment laws. I want to emphasise the fact that we go into these investigations with an open mind and a degree of confidentiality."
Mr Burden said he was yet to speak to the student about the allegation.
"We have a policy that we talk to everyone involved, and be a little bit forensic about it. We've got to talk to adults from both sides, people have got to sign statements and so forth."
Fallon told the Weekend Herald he couldn't talk about the incident, saying: "No I can't and I won't because there is an inquiry about it all. It's all being put into perspective. I've got nothing to add at all. Write what you want."
The principal's secretary at Auckland Grammar said: "We really don't have any comments because it's not us laying the complaint."
New Zealand Secondary Schools Football chairman Malcolm Cowie said the association was not involved.
Colourful history
* September 2012: A complaint is made by a parent that he made offensive comments to a rival player
* August 2009: Banned for a season because of complaints he accused ref Alan Marriott of being biased
* September 2008: Auckland Grammar pulls out of the final with MAGS after allegations Fallon "man-handled" a player during a brawl