Adam Johnson has been sacked by Sunderland after pleading guilty to one count of sexual activity with a child and one charge of grooming.The 28-year-old footballer`s contract was terminated hours after he was dropped for Saturday`s Premier League match against Manchester United.He will stand trial on Friday on two further counts of sexual activity with a child, which he denies.Sportswear firm Adidas has cancelled its contract with the midfielder.After Johnson`s arrest in March 2015, the club suspended him, but then lifted the ban following talks with his representatives and the Professional Footballers` Association.In his last appearance for the Black Cats, England international Johnson - who played while on bail - scored in a 2-2 draw against Liverpool at Anfield.Johnson, who was born in Sunderland, began his career at Middlesbrough before moving to Manchester City and then to Sunderland for £10m in 2012.When asked about the winger`s future at a news conference earlier on Thursday, Sunderland manager Sam Allardyce said: "He`ll not be available for this weekend. We will see how it goes after that."Johnson`s trial, to be held at Bradford Crown Court, is expected to last two weeks. -BBC