Police in Derry have arrested a man in his 20s on suspicion of grevious bodily harm.
It follows a report of an assault outside licensed premises in the Waterloo Street area at around 9 pm on Wednesday night.
A man in his 30s is currently in a critical condition in hospital.
The arrested man remains in custody helping police with their enquiries.
Officers want anyone who witnessed the incident or who has any information to contact them in CID at Strand Road on the non-emergency number 101.