A Spanish court has opened an investigation into allegations former Brazil defender Dani Alves sexually assaulted a woman at a Barcelona nightclub last month.

A Barcelona court opened a probe "into an alleged crime of sexual assault as a result of a complaint filed by a woman against a football player," the Superior Court of Catalonia said in a statement.

While the statement did not name Alves, informed sources confirmed to AFP the former Barcelona and Juventus player was the subject of the investigation.

Catalan police said they had received a complaint on January 2 from a woman who said Alves had touched her inappropriately.

The alleged sexual assault took place at a popular Barcelona nightclub overnight December 30-31, according to Spanish media reports.

The player was accused of putting his hands down the woman's pants, according to the reports.

Alves, 39, has confirmed he was at the night club at the time but has denied any wrongdoing, telling private Spanish television Antena 3 last week that he has "never seen" the woman before.

"I was there, at that place, with more people having fun. Everybody knows I love to dance. Having a good time but without invading the space of others," he added.

Alves, who now plays for Mexican side Pumas UNAM, was in Barcelona on holiday following his participation at the World Cup with Brazil in Qatar.

He was the oldest player to represent Brazil at the men's World Cup.