O’Neill, 61, was sacked by Sunderland’s American owner Ellis Short on Saturday night, shortly after a 1-0 defeat at home to Premier League leaders Manchester United.
The result extended Sunderland’s run of games without victory to eight and left the north-east side just a point above the relegation zone with seven games of the season remaining.
Former Crystal Palace and Reading manager Steve Coppell pointed the finger at the short-term approach adopted by club owners in the English top flight.
“For me, I can only think there was a personal confrontation after the game as Martin, in his interviews after the game, looked calm, collected and inspired for the challenge ahead,” Coppell told BBC Radio Five Live.
“We are in the realms, I’m afraid, of spoilt-brat reactions because it is their (the owner’s) toy.
“They don’t understand the history and heritage of British football. There are so many foreign owners. I have nothing against that, but there is a way of doing things in English football that has now gone out of the window.”
Former England striker Alan Shearer said he was surprised by the timing of O’Neill’s departure.
“It’s bizarre. They have gone down the route that Reading have (sacking Brian McDermott),” he said on BBC television programme Match of the Day.
“They are on a terrible run of form but it is the timing of it I find hard.”
Stan Collymore, who played under O’Neill as a striker at Leicester City, said the Northern Irishman may have struggled without his former assistant John Robertson, with whom he had worked at his previous clubs.
“John Robertson was the conduit between player and manager,” Collymore told talkSPORT radio station.
“He would watch training, perhaps go in a couple of times to see the manager, who probably wouldn’t even come out until the last 10, 15 minutes of the session, where everything got much livelier.
“Because it was unusual for the gaffer (manager) to come out and oversee training – like Sir Alex Ferguson or like David Moyes – and what John Robertson would do would be to report back.
“Who’s looking sharp, who’s not looking so sharp, and I think in terms of this season, Martin O’Neill just hasn’t looked himself.
“He hasn’t had that sounding board with John Robertson.”
One-time England manager Steve McClaren has been installed as the early favourite to succeed O’Neill at the Stadium of Light, with former Swindon Town coach Paolo Di Canio also reported to be in the running.
Sunderland are expected to make an announcement about the vacancy prior to their trip to Chelsea next Sunday.