"He is looking forward to getting back into training with his team and will just have to wait for the police to get back in touch when they have completed their investigation."
Connacht, which Muliaina joined at the beginning of the Northern Hemisphere rugby season last year, had not stood down the 100-capped player, Mr Porter said.
A spokesman from Italian club Zebre, which has contracted Muliaina for next season, said it was aware of the allegation, but had no comment.
Few details about the alleged incident have been released.
When police picked him up after his team's 14-7 defeat to Gloucester in the Challenge Cup on Saturday, the fullback believed he was being collected for drug testing. However, he was driven back to the Welsh capital for questioning over an alleged sexual assault in Cardiff last month.
Connacht played the Cardiff Blues in the city on March 6, but police did not say what date the alleged incident is said to have occurred.
Muliaina, who agreed to return to Cardiff for questioning in July, has not been charged and was released on police bail.
Busker Brownes, the Galway pub which sponsors him as a Connacht player, said yesterday it had no comment to make on the matter. When asked whether the pub would withdraw sponsorship, it again refused to comment.
Hayley Muliaina, the player's estranged wife and mother of his 6-year-old son, was not at the Grey Lynn home the pair own last night.
The story so far
• March: Alleged sexual assault incident involving Mils Muliaina is believed to have occurred.
• March 6: Muliaina's Irish team Connacht play the Cardiff Blues in Cardiff. The team enjoy a night out drinking after the match.
• April 4: Welsh police arrest Muliaina at Kingsholm Stadium in Gloucester after his team lose 14-7 to Gloucester in the Challenge Cup. He is taken into custody over an alleged sexual assault involving a 19-year-old woman in Cardiff in March. Muliaina is taken back to Wales where he spends the night in a police cell and is questioned about the allegation.
• April 5: Muliaina released on police bail. No charges have been laid. He agrees to return to Cardiff for further questioning in July.