The 25-year-old, who spent last year on loan with Burnley, was captured on CCTV footage in Liverpool city centre beating and kicking Rachael Wall, his girlfriend of 18 months.
Judge Wendy Lloyd told Flanagan he could expect a community sentence.
“I need to be reassured that these circumstances will never be repeated again,” she said.
Flanagan’s lawyer Lionel Greig said Wall had not provided a statement and there had been no previous instances of domestic violence in their relationship.
He said both Flanagan — who won his only England cap in a warm-up friendly prior to the 2014 World Cup — and Wall were under the influence of alcohol at the time of the incident.
Flanagan came through Liverpool’s academy system and made his senior Reds debut in 2011, though he has played just once this season in the League Cup.
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