Mackay, who guided Cardiff to the Premier League after a 51-year wait, was sacked by the club's owner Vincent Tan in December 2013, two months after Moody was dismissed.

Cardiff on Thursday declined to make any public comment on the dossier and the matter is now in the hands of the FA.

The FA has confirmed it has received a detailed account of issues related to Mackay and Moody, now director of football at Crystal Palace.

An FA spokesman said: "The FA can confirm it is currently investigating this matter."

News of the existence of the dossier, which appeared first in The Daily Mail, appears to have closed the door on Mackay succeeding Tony Pulis as Palace manager, according to Britain's Press Association.

Caretaker Palace boss Keith Millen is now expected to take charge of Saturday's home Premier League clash with West Ham.

Palace declined to comment on the situation regarding both Mackay and Moody.

Earlier this week Palace were fined by the Premier League for their part in the 'spygate' saga involving Cardiff last April.

The Premier League determined that Palace had breached their 'good faith' rule by obtaining information about Cardiff's team ahead of their 3-0 win when the two clubs were relegation rivals.

The Welsh club had complained to the Premier League that Moody had contacted Cardiff employees for information in the build-up to the game.