Former All Blacks star Mils Muliaina has been cleared of sexual assault after being wrongly accused of touching a woman's bottom in a nightclub in Wales.

The 35-year-old, who now plays for Italian Pro12 side Zebr, was charged in July following an alleged incident said to have occurred four months previous in Cardiff.

The accusation came to light in April when Muliaina was arrested just minutes after his club Connacht lost to Gloucester in the European Challenge Cup.

This week, a judge ruled that there was not enough evidence that the New Zealand rugby legend had grabbed the unnamed clubber's backside.

"It's been incredibly frustrating not to be able to publicly comment about it," Muliaina told reporters. "While I understand the police have a job to do, the manner in which I was arrested I find difficult to understand.

"I can still hold my head up high and, as the judge said, this is no stain on my character. I have always known that I did not do anything wrong. I don't even know the woman and I don't know what happened, but I wasn't the person who had done what she said had happened."

Defending counsel John Charles Rees QC told Judge Eleri Rees: "My client is a professional athlete whose reputation has been reduced while the complainant remains anonymous. The allegation was that her bottom had been fleetingly touched on a busy nightclub dancefloor. He has denied doing anything wrong from beginning to end."

Muliaina scored 33 tries in his 100 appearances for New Zealand.