David O'Leary fell into League One after three years .
O'Leary 's departure signalled a downhill spiral for the club - highly attributable to the financial state that saw the sale of several key players - which would see three more managers ( Venables , Peter Reid and Eddie Gray ) come and go before the club was finally relegated from the Premiership in 2004 with £80 million debt , and fell into League One ( the third tier of the league ) three years after that .