England international Adam Johnson pleaded guilty to one count of sexual activity with a child, but denied two other charges, when he appeared at Bradford Crown Court on Wednesday.
The 28-year-old Sunderland winger, who has played 12 times for England, also admitted one count of grooming a girl under the age of 16, a court official said.
Johnson, who began his career at Middlesbrough and also played for Manchester City, joined Sunderland for 10 million pounds in 2012 on a four-year contract.
He has been a regular for the Premier League side this season and scored in the 2-2 draw with Liverpool last week.
The case is expected to last for two weeks.