Senior sources say that officers are satisfied that Mr O’Neill was the victim of an assault
Senior sources say that the suspect in custody who is aged in his 30s is known to the victim.
Detectives launched an investigation after the body of the man was found in his property at St Brendan's Road in Lisdoonvarna, Co Clare.
Gardai were alerted to the incident at around 8am today by a phone call and are not looking for anyone else at this stage in relation to the incident.
Senior sources say that officers are satisfied that Mr O’Neill was the victim of an assault and that the suspect had been a regular visitor to his home.
“This is not a murder investigation yet – the suspect has been arrested in relation to an assault and he can be detained for 24 hours in relation to that accusation.
“A post mortem on the deceased will determine what way this investigation goes,” a senior source said.
A garda spokesman said earlier a man has been arrested in connection with the incident.
"The man is currently detained in Ennis Garda Station under Section 4 of the Criminal Justice Act, 1984.
"The scene is currently preserved and a technical examination is being carried out by the Garda Technical Bureau. State Pathologist Margaret Bolster has attended the scene.
"The body of the man has been removed to University Hospital Limerick where a post-mortem will take place. The results of this post mortem will direct the course of the investigation."
A source previously told the Sunday World: “The early indications at this stage is that foul play was a factor in this incident. This is a situation that appears to be very much more than a fall or something like that."
Gardaí commenced door to door inquiries in the area in a bid to determine the last known movements of the deceased.
Detectives appealed for anyone with any information in relation to the matter to contact Ennistymon Garda Station on 065 707 2180, the Garda Confidential Line on 1800 666 111 or any Garda station.