John Pender, who was in his 50s, was on holiday on the Costa del Sol with his family when he was attacked in a bar in Fuengirola.
The British man, who is understood to have been living in Spain, was arrested at the scene.
Tributes have been paid to Mr Pender who was from the Shankill area of Dublin.
The father-of-two worked with the Suicide or Survive charity, which said it deeply regretted the loss of their "beautiful friend and colleague".
St Joseph's Boys AFC, which is based in Sallynoggin, also paid tribute to Mr Pender.
In a statement on its Facebook page, the club described him as a "wonderful, compassionate, empathetic man who helped so many former players and coaches and many, many others in the wider community, not just through his work with the charity Suicide or Survive but by being John".
It said those who knew him are completely and utterly stunned at his death.