Sydney Roosters hooker Mark Riddell has announced his immediate NRL retirement, ending an 11-year career at the top level.

The former St George Illawarra and Parramatta star, who also had a two year stint with Wigan in the English Super League, announced his decision on social networking site Twitter on Saturday.

Riddell said it was not related to any injury concerns, and that he would stay on at the Bondi club in an official role to help coach Brian Smith.

The Roosters signed Eels hooker Anthony Mitchell during the week on a mid-season transfer and already have outstanding prospect Jake Friend who has made the No.9 jersey his own this season.

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