St George star Jack De Belin has been released on bail after being charged with sexually assaulting a 19-year-old woman with another man.

The 27-year-old lock was charged with aggravated sexual assault in company when he went to Wollongong Police Station yesterday afternoon.

A 19-year-old woman told police De Belin was one of two men who she claims sexually assaulted her at an apartment in Wollongong, south of Sydney, in the early hours of Sunday morning.

De Belin has notified his partner, who is 20 weeks pregnant. (9NEWS)

The alleged victim told police she got into a Pedi Cab with De Belin and another lower grade player after a night out at an establishment on Crown Street.

She claims they told her they were going to another venue, but instead took her to the apartment block so they could change clothes.

The 19-year-old said she went upstairs to use the bathroom and when she came out the pair were naked. She alleges this is when she was sexually assaulted.

The woman got medical treatment at a local hospital after telling a girlfriend what had happened.

Jack De Belin is being investigated over sexual assault allegations. (AAP)

De Belin has told club officials he is innocent and denies any kind of assault.

St George Dragons released a statement confirming officials were aware of the charges, adding that De Belin had been provided welfare support.

“The club is taking the matter very seriously and have been working with Jack and all relevant authorities, including police and the NRL integrity Unit,” the club said in a statement.

“As this is a police matter to be considered by the court, the club is not in a position to make any further comment at this time.”

Jack De Belin was selected to play in all three Origin Games this year. (AAP)

The Origin player has discussed the matter with his partner, who is 20 weeks pregnant.

He was released from Wollongong Police Station on conditional bail last night.

Former Dragons coach and player Craig Young started making enquiries about the allegations three days ago.

9News does not suggest De Belin is guilty, only that an investigation is taking place.