The incident is said to have happened on Bank Hey Street at around 2.05am on May 5.
Officers investigating the attack have released CCTV footage of a man they wish to speak to in connection with the incident.
If you recognise the man or have any information that may assist police, call 101 quoting log 0115 of 5 May.
Information can also be reported online via the Lancashire Police website at https://doitonline.lancashire.police.uk/.
Alternatively, independent charity Crimestoppers can be contacted anonymously on 0800 555 111.
