The Queens Park Rangers midfielder, 29, was involved in trouble in the early hours of Monday morning while on a night out with his girlfriend in Liverpool city centre.
Two men were arrested at the scene, outside Garlands nightclub, and Barton and a 20-year-old man were arrested on Monday afternoon. All have been bailed. After his release, Barton said via Twitter: "Looking forward to Portugal now tomo. Bit of rest and lots of golf..."
Two men, aged 21 and from the Old Swan area of Liverpool, were arrested on suspicion of a public order offence at around 5.30am at the scene of the incident. Barton was released on bail on Monday night by Merseyside Police pending further inquiries. The three other men were bailed earlier.
A statement from the force said: "Merseyside Police can confirm that the 29-year-old man arrested on suspicion of affray has been released on bail pending further inquiries."
Earlier on Monday, the Liverpool-born midfielder confirmed the incident by tweeting: "I got sucker punched in the back of the head. Not injured as reported just a small bruise on rear of head/ear. I've had worse. Life goes on! Thanks for the concern. Have a good day people."
Later he tweeted: "Not planning on pressing charges as it's not that serious. The police have also got better things to do with their time. Can I just say a public thanks to the police last night as they were and have been today brilliant."
A picture of the incident, apparently showing a shirtless Barton being held back by police and a woman, also began to circulate on Twitter.
The player is under investigation by his club after he was given a 12-match ban by the Football Association. He was banned by English football's governing body after being sent off during QPR's defeat at Manchester City on the final day of the Premier League season.
In a statement, QPR spokesman Ian Taylor said: "Barton was on his way home from a night out with his girlfriend when two men sang offensive chants and then proceeded to hit the QPR midfielder."