Barton arrested over nightclub incident
A spokesman for Merseyside Police said four men had been questioned, two of them over a public order offence.
"Following an altercation in Eberle Street, Liverpool city centre, in the early hours of this morning, four men have been arrested on suspicion of affray," a police statement said.
"Two 21-year-old men were arrested at the scene in the early hours of this morning and another two men, a 20-year-old from the Liverpool area and a 29-year-old from the Widnes area, were arrested this afternoon."
The police added that all four men were later released on bail pending further enquiries.
The Liverpool-born Barton, 29, will serve a 12-match ban at the start of next season after being found guilty of violent conduct following his sending-off in QPR's final Premier League game of last term against his former club Manchester City.