A Prison Service spokesman said ex-Manchester City youth player Courtney Meppen-Walter was released "in error" and added that such incidents are taken "extremely seriously".
Police have been informed after a prisoner was released in error on Monday July 1 to ensure he is promptly returned to custody.
Releases in error are very rare and we take any incident extremely seriously. An investigation will take place into the circumstances that led to this release.
Meppen-Walter wept in court when he was jailed at Manchester Crown Court on February 28.
More top news
The double Grand Slam winner said he did not regret giving his opinion, but was 'disappointed' at the way he went about it.
It seems the Prime Minister is waiting to have talks with other world leaders in New York where he is attending the UN General Assembly.
Rio Ferdinand has emerged as a surprise possible choice to be the FA's candidate for Britain's FIFA vice-presidential position