The victim, who is in his 40s, sustained head injuries in the attack outside a licensed premises in Flax Street at about 05:25 BST.
He was taken to hospital and a police spokesman said he is "said to be in a critical but stable condition".
Det Insp Heather Whoriskey appealed to anyone who was in the area at the time to come forward with information.
A man is critically ill after he was attacked by a number of people in an overnight assault in north Belfast.