An engagement party at the towns Railway Institute ended on sour note after a fight involving a number of people started outside the club.
The police were called to the club at 11 pm on Saturday night and found a 35 year-old Southampton man who had been assaulted after he intervened to break up the fight.
He had suffered a number of face and head injuries and was treated initially by paramedics and then at Southampton General Hospital.
Police have been continuing their investigation, including reviewing CCTV from the club and the town centre and speaking to a number of the 100 guests who are known to have attended the event.
A spokesman for Eastleigh Police said:
“I’m appealing to those who attended the event who have information to come forward. We know a number of people saw what happened last night and for whatever reason may be reluctant to tell us what happened. Please contact Eastleigh police on 101 or you can give information anonymously via crimestoppers on 0800 555 111. This was type of incident at the Railway institute is very rare and I’m confident we will find those responsible.”