Detectives are appealing for information in relation to the reported assault in the Bank Place area of Derry.
A man has been arrested in connection with the alleged assault.
A PSNI spokesperson said: "Shortly before 1.10am, police received and responded to a report of a male being assaulted in the area.
“Officers attended the scene, and discovered a man lying on the ground. He was subsequently taken to hospital by NIAS crews for treatment, where he remains in a stable condition at this time.
“It is believed that the assault took place at approximately 12.50am.
“A man in his 30s has been arrested in connection with the incident, and remains in police custody at this time, assisting with enquiries.
“Our enquiries are continuing, and I am appealing to anyone who was in the area at the time of the incident, and may have any information which could assist, to call 101 and quote reference number 56 of 25/01/22.”
You can also submit a report online using the non-emergency reporting form via http://www.psni.police.uk/makeareport , or contact Crimestoppers anonymously on 0800 555 111 or online at http://crimestoppers-uk.org