The incident took place at the The Golden Hind pub on Copnor Road at around 5pm.
A statement from Hampshire Constabulary said: ‘A 55-year-old man from Portsmouth was arrested on suspicion of causing grievous bodily harm with intent and has been released but remains under investigation’.
The victim was said to be in his 40s.
A photo taken outside the pub last night showed two police cars which had been called out.
You can catch up with more of our stories about crime and incidents in Portsmouth by joining our Portsmouth Breaking News and Incidents Facebook group.