The 36-year-old was arrested after police were called to his team's hotel in Croydon, south London, on December 3 last year, the night before his team's FA Cup match against Sutton United.
He pleaded guilty at Croydon Crown Court on Friday to a charge of common assault at the Aerodrome Hotel in Purley Way.
Hughes, of Waterside Way, Nottingham, was fined £500 and ordered to pay £120 in prosecution costs. He has 28 days to pay the fine or could face 14 days' imprisonment.
A second charge of sexual assault, which Hughes denied, was dropped after prosecution lawyers offered no evidence.
The footballer, who previously played for West Brom in the Premier League, was jailed in 2004 for causing death by dangerous driving.
Douglas Graham, a 56-year-old father-of-four, died after Hughes' Mercedes ploughed into the Renault in which he was a passenger.
After Hughes was released from prison in 2007, the striker restarted his football career at Oldham before joining Notts County in 2009.
A CPS spokeswoman said: "Following a further review of the evidence available in this case, the Crown Prosecution Service has concluded that there is no longer a realistic prospect of conviction for a charge of sexual assault and accordingly we have offered no evidence.
"At Croydon Crown Court today Lee Hughes pleaded guilty to one count of common assault and he has been sentenced to a £500 fine and ordered to pay £120 in costs."