The incident occurred in Athlone last Friday night.
Gardaí are renewing their appeal for the good samaritan who intervened in an assault in Athlone at the weekend to come forward.
The serious attack on a woman took place near the River Shannon at Athlone Castle between midnight and 12.30 last Friday night.
The attacker fled the scene when another man came to the aid of the victim.
One man was arrested in relation to the incident and has since been released without charge, pending a file to the DPP.
Sergeant in Charge at Athlone Garda Station, Andrew Haran, says gardaí are looking to get information off the man who came to her assistance, or anyone else who witnessed the incident:
Anyone with information is asked to contact Athlone Garda Station on 090 6498550 or the Garda Confidential Line on 1800 666 111.