Malky Mackay allegedly sent texts of a racist, sexist and homophobic nature during his time as manager of Cardiff City.
The Welsh club, who sacked Mackay in December, have sent a dossier to the Football Association with details of the allegations, football's governing body have confirmed.
An FA spokesman said: "The FA can confirm it is currently investigating this matter."
News of the allegations have come quickly after it emerged the Scot would not be taking over at Crystal Palace. Mackay had been the favourite to replace Tony Pulis at Selhurst Park but he is no longer in the running.
His relationship with Palace's sporting director Iain Moody, who worked as head of recruitment at Cardiff during Mackay's time in Wales, was considered to be in his favour. However, Moody has also allegedly been accused of wrongdoing by Cardiff.
The Daily Mail claim two letters have been sent to the FA by Cardiff City outlining a series of texts. The Daily Mail claims the following messages were sent.
'Fkn chinkys. Fk it. There's enough dogs in Cardiff for us all to go around.'
On the arrival of South Korean international Kim Bo-Kyung
'Go on, fat Phil. Nothing like a Jew that sees money slipping through his fingers'
On football agent Phil Smith
'He's a snake, a gay snake. Not to be trusted'
On an official of another club
'Not many white faces amongst that lot but worth considering.'
On a list of potential signings
'I hope she's looking after your needs. I bet you'd love a bounce on her falsies.'
On a player's female agent
A picture entitled Black Monopoly (where every square was a "Go to Jail" square)
Sent to members of Cardiff's staff
It is understood Crystal Palace owner Steve Parish became aware of the allegations following Mackay's departure from his previous club and in particular his longstanding row with the club's controversial chairman and owner Vincent Tan.
Who will be the next Crystal Palace manager?
Who will be the next Crystal Palace manager?
1/9 Neil Lennon
The current favourite has been out of management since stepping down from Celtic in May after four years in charge in Glasgow, his first job in management. Lennon, who led the Bhoys to the title in each of the last three seasons, is a fiery character on the sideline, often getting into spats with referees and SFA officials.
2/9 Keith Millen
Has had four spells as a caretaker manager at Bristol City and Palace but only one full season in the top job, at City in 2010-11. Taking over from Steve Coppell, who left just one game into the season, City eventually came 14th under Millen’s guidance.
3/9 Steve Clarke
Has jumped from a rank outsider to the second favourite to take over at Selhurst Park; Clarke was seen as harshly treated by many when he lost his job at West Brom in December 2013. The previous season they had finished 8th in the Premier League, but ended that campaign badly and started the next one even worse. He has plenty of experience as an assistant with stints at Newcastle, Chelsea, West Ham and Liverpool.
4/9 Martin Jol
Another former Spurs manager, Jol’s big reputation took a significant knock after he was sacked from Fulham in December following six successive defeats. If he were appointed Palace would like the man who almost led Tottenham to the Champions League rather than the one that led Fulham to relegation.
5/9 Dermot Drummy
A relative unknown, Drummy once had a contract with Arsenal but failed to play a league game for the Gunners before bouncing around non-league clubs. When he retired from playing at 35, he returned to north London as a coach, starting with the Under-16s, working with the likes of Jack Wilshere and Kieran Gibbs. He moved to Chelsea’s Under-16s and worked his way up the ladder, eventually taking charge of the Youth Team, then the reserves. Drummy was recently appointed to the role of international head coach
6/9 Phil Brown
The former Hull City boss is currently at Southend United, where he led the Shrimpers to the play-offs last season after years in League Two obscurity. Brown is best known for leading Hull to the Premier League, though some eccentricities, such as singing to fans on the day the club stayed up and holding a team talk on the pitch, have overshadowed the job he did at the club.
7/9 David Moyes
Manchester United still seem to be feeling the ill-effects of the Scot’s reign at Old Trafford. But Moyes got the job in the first place because he had been a brilliant manager at Everton for a decade, taking the club from relegation fodder to perennial top six contenders. Roberto Martinez’s success last season has futher tarnished Moyes’ legacy, but he remains a skilled manager.
8/9 Glenn Hoddle
The former England manager has not managed any side since he left Wolves in 2006, spending the intervening years as a television pundit. Hoddle returned to football earlier this month when Harry Redknapp named him as a first-team coach at QPR. The Independent understands he has ruled himself out of the running.
9/9 Roberto Di Matteo
Best known for a highly eventful spell in charge of Chelsea, where he won the FA Cup and the Champions League before getting sacked at the start of the next season, Di Matteo also had good spells as manager of MK Dons and West Brom.
Mackay was furious when he was sacked by Tan in December and immediately demanded compensation for breach of contract, making his feelings clear about the Malaysian billionaire. he later issued a public apology to Tan, praising his work for Cardiff and abandoning his claim for compensation.
What motivated Mackay's change of heart remains unclear but it is suspected the details may have persuaded Palace to rule out the Scot.