Three men, aged 26, 32 and 34, were found after a fight broke out near Junk nightclub in London Road at about 04:00 GMT on Friday.
Two of the men had knife wounds, while a third suffered a head injury.
Four men from the London area, aged between 19 and 21, who were arrested on suspicion of grievous bodily harm and affray, have been bailed until 7 April.
Four men who were arrested in connection with a stabbing in Southampton have been released on bail.