Sunderland have been cut to 9/4 for Premiership relegation after a Ladbrokes shop punter in Ireland had a 20,000 Euro bet on the Black Cats to go down.
The customer stands to win 50,000 Euros if the managerless team fail to escape the drop zone having taken odds of 5/2 within moments of Roy Keane's departure.
David Williams of Ladbrokes said: "The big staking punter is convinced that Sunderland without Keane are doomed."
In the next managerial market, early 2/1 favourite Sam Allardyce has been cut to 6/4 as punters anticipate a return to the North-East for the ex Newcastle boss.
"Often the early money comes for an outsider who's not been on our radar but Big Sam is attracting all the early attention" said Williams.
Ladbrokes latest betting
Premiership relegation
1/5 West Brom
4/7 Stoke City
9/4 Blackburn Rovers
9/4 Sunderland (from 5/2 at lunchtime, Thursday)
3/1 Bolton
3/1 West Ham
4/1 Newcastle
4/1 Hull
9/2 bar
Next permanent Sunderland manager (correct as of Thursday evening)
6/4 Sam Allardyce (from 2/1)
5/1 Alan Curbishley
8/1 Phil Brown
10/1 David O'Leary
10/1 Steve Bruce
12/1 Avram Grant
12/1 Gordon Strachan
12/1 Ricky Sbragia
16/1 Dick Advocaat