Australian Test cricketer Glenn McGrath is caught in an alleged $15,000 extortion bid in which a former friend of his mother's demanded cash for private letters.

A former colleague of McGrath's mother Bev, Peter Amiet, told the Daily Telegraph he was in a tight financial situation and needed to make some money, so he'd contacted the cricketer's manager to arrange a deal.

"I have done nothing wrong. I didn't want to hurt Glenn or Beverley so I went to the manager instead," Mr Amiet told the newspaper.

"I need to get out of some financial trouble but I haven't broken the law."

When McGrath's manager Warren Craig refused the demand for $15,000, Mr Amiet said he had "no choice" but to post the letters for sale at online auction site eBay.

The private letters, which Mr Amiet said were addressed to him and obtained legitimately during his friendship, in 1993, with Mrs McGrath, included details of her marriage to Glenn's father Kevin, and other personal matters.

NSW police said the items had been removed from eBay and the matter referred to the robbery and serious crime squad for investigation as a potential extortion bid.

Mr Craig said McGrath - who was expected to return from England on Wednesday evening following the crushing Ashes loss - was aware of the letters, but was not "fully across it".

He could not confirm whether or not they were authentic.

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