Two men who were arrested on suspicion of serious assault after an incident in Kettering on Saturday, June 1, have been bailed.
CID officers were at the scene on Sunday to investigate the attack, in which a 41-year-old man suffered a serious head injury.
Northamptonshire Police say he is in a critical condition at Walsgrave Hospital in Coventry.
The incident occurred following a disturbance in the street, police have said.
A 26-year-old and a 19-year-old were arrested by police.
They were in custody in Corby, but police have since said they have been bailed pending further inquiries.
Anyone with any information should call police on 101 or give information anonymously to Crimestoppers on 0800 555 111.