I don't think anyone is going to disqualify him for not having one.
In fact I have no idea who is the final arbiter of whether or not a presidential candidate is a natural born U.S. citizen and what the official legal process would be to challenge someone's citizenship in running for president.
I don't think it's been remotely an issue in modern history. And I would doubt that more than 1/3rd of Americans know that you have to be a native-born citizen to be President.