The 28-year-old player, capped 12 times by England, continues to deny two other charges of sexual activity with a girl aged under 16.
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Johnson appeared in the dock at Bradford Crown Court in northern England. He was accompanied by a female police officer.
He was initially suspended by Sunderland following his arrest in March last year, but has since returned to action and scored in their 2-2 draw at Liverpool in the Premier League last Saturday.
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Johnson began his career with Middlesbrough and returned to his native northeast in 2012 when he joined Sunderland from Manchester City in a £10 million deal.
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