New Zealand businessman and Warriors boss Eric Watson was Australian actress Nicole Kidman's "mystery man" at a recent boxing bout in the US, the Australian Herald Sun website reports, citing an unnamed US weekly magazine.

It's not clear whether the pair are dating, but they have been spotted in each other's company before the world middleweight boxing championship fight in Las Vegas.

There, they watched the challenger's Oscar De La Hoya's defeat at the hands of Bernard Hopkins at the MGM Grand.

Kidman and Watson were both among high-profile guests, including New Zealand-born actor Russell Crowe, who attended Wollongong Entertainment Centre in January to watch Australian boxer Anthony Mundine defeat Japanese boxer Yoshinori Nishizawa.