North Wales Police found the 27-year-old unresponsive outside Peep on Dean Street, Bangor, shortly before 02:00 BST on Saturday.
Officers carried out CPR before he was taken to hospital, where he died on Sunday morning.
A 26-year-old man, arrested in connection with the assault, has now been arrested on suspicion of murder.
The family of Mr Ayabowei, a father-of-two from the Llangefni area, has been informed.
He had initially been taken to Ysbyty Gwynedd Hospital, but was transferred to a hospital in Stoke where he later died.
In a statement on its Facebook page, Llanfairpwll football club paid tribute to Mr Ayabowei - also known as Henry Esin - who had been one of their players, saying he was a "true gentleman in every sense".
Det Ch Insp Brian Kearney said: "A major incident room has been set up at Bangor police station, and a team of detectives are continuing to establish the full circumstances leading up to the victim's tragic death."
Insp Owain Llewellyn said: "I am deeply shocked and saddened by the tragic death of this young family man.
"The thoughts of our community are with his wife, children and friends.
"Whilst incidents of this nature are very rare, and North Gwynedd is one of the safest parts of the United Kingdom, we will continue to work closely with our licensees, businesses and our partner agencies to prevent such tragic events."
A father who died after being assaulted outside a nightclub in Gwynedd has been named as Henry Ayabowei.