They also allege he attempted a "shakedown", threatening negative coverage unless they paid him $15m (£11.8m).

Michael Oher earlier this week accused Sean and Leigh Anne Tuohy of lying when he signed papers making them his conservators as an 18-year-old.

He said he was told it would make them his adoptive parents - when it did not, and that he didn't understand he was "signing away" his rights.

Oher claims the family profited by selling his story - which became 2009's The Blind Side starring Sandra Bullock - and says he made nothing from it.

He wants compensation and an end to the conservatorship - an agreement allowing someone to take legal guardianship over an adult.

Oher claimed he only found out in February that the conservatorship "provided him no familial relationship".

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The 37-year-old played eight seasons in the NFL after being drafted in 2009 and won a Super Bowl with the Baltimore Ravens.

A statement for the Tuoys said his accusations were "absurd", and claimed that before he started his legal action he demanded $15m from them.

Randall Fishman, a lawyer for the Memphis couple, told reporters on Wednesday: "To say they were devastated by these allegations is truly an understatement... They would never do anything to deprive Michael of anything that was his."

The family claimed in their statement to be worth "hundreds of millions of dollars" and said they wouldn't have tried to cheat Oher.

They said they negotiated a small advance and a "tiny percentage" of the film's profits - to be divided equally between Oher and family members - with cheques and statements said to back this up.

Oher allegedly refused to cash the cheques, so they put the money in a trust account.

"They have consistently treated him like a son and one of their three children," the statement added.

Mr Fishman said the couple now intend to end the conservatorship - and that it had been set up to help Oher with health insurance, a driver's licence and getting into university.