New Zealand Prime Minister John Key has refused to deny that he described Los Angeles Galaxy midfielder "thick as bat shit".

Key is alleged to have made the comments during a recent trip to a school in Auckland, where he was discussing the former England captain in a private conversation.

"That is someone that thinks they have overheard a conversation I have had," Key said on breakfast television. "I am not going to engage in that because otherwise I am engaging in every conversation that someone thinks I have."

When the presenter asked if the politician could clarify that he didn't call Beckham "thick", Key replied: "No, what I am saying is that somebody has overheard a personal conversation and that's their recollection of it. I am just not going to engage in discussions about that. That's their view."

The 37-year-old has played for LA Galaxy since 2007.