The man in his 30s was found with serious head injuries in Haig Avenue, Chatham at about 22.55 BST on Tuesday.
Police believe he was attacked during a disturbance in Glencoe Road and Magpie Hall Road, minutes earlier.
A 26-year-old local man arrested on suspicion of attempted murder remains in custody.
Kent Police have also held a 27-year-old woman, also from the town, on suspicion of assisting an offender.
Det Insp Ivan Beasley said: "The victim remains in a very serious condition in hospital with life-threatening injuries."
A man has been arrested on suspicion of attempted murder after a man was critically injured in a "disturbance" involving several people.