A legal expert says boxing fans disappointed with last weekend's fight of the century might be entitled to a refund.

Punters are suing boxer Manny Pacquiao, claming they were left out of pocket by his failure to disclose a shoulder injury during his fight against Floyd Mayweather.

Otago University law professor Rex Ahdar says there may have been a breach of the Fair Trading Act.

He says New Zealanders might be able to ask their pay-per-view provider for a refund.

MORE: Full interview with Rex Ahdar

"I would try that letter first, before you even start thinking about class actions where you get a lawyer to represent hundreds or thousands of you."

Lawyers pursuing the class-action suit in the USA want $5 million in damages.

It's just the latest fallout from Mayweather's victory in Las Vegas in a unanimous decision, with Pacquiao saying afterwards that the shoulder complaint hampered his performance in the welterweight world title showdown.

And while the boxing match billed as the fight of the century is over, the battle over smartphone video streaming of the showdown is just beginning.

Revelations that dozens of smartphone users streamed the Manny Pacquiao-Floyd Mayweather weekend fight have raised questions about how new technologies can get around copyright restrictions imposed at live venues.

There are no reliable figures, but thousands of people may have watched the fight via the Twitter-owned app Periscope and independent app Meerkat.

These viewers avoided the $100 US fee for official pay-per-view video - as long as they didn't mind reduced picture quality.