The jury was discharged after being unable to agree following 25 hours, 23 minutes of deliberation.
The five men and seven women were only able to agree one verdict, finding Lewis Dunk not guilty of voyeurism.
Brighton players Anton Rodgers, 20, Lewis Dunk, 21, and George Barker, 21, and former team-mate Steve Cook, 21, who now plays for Bournemouth, had pleaded not guilty to sexual assault and voyeurism.
They were alleged to have assaulted a 19-year-old woman in a Brighton hotel room in July 2011.
The woman claimed she fell asleep following a drunken night out clubbing and saw photographs of the incident on Rodgers' mobile phone in the morning.
The players told the Old Bailey there was nothing sexual in what went on and the woman was awake during most of the "boy banter".
Prosecutor Richard Barton told the court he would seek a retrial, provisionally set for April 22, after discussing it with the complainant.