Martin O'Neill has hit back at Paolo Di Canio with the spat between the two former Sunderland managers showing little sign of abating.

The Ulsterman, who was replaced by the Italian following his own sacking by the Black Cats in March, described his successor as a “managerial charlatan” following a sustained attack on his regime during his stint at the Stadium of Light.

Di Canio responded in a television interview on Friday, instead accusing O’Neill of being the charlatan and decrying his transfer dealings in particular.

But speaking after his side's 3-0 friendly victory over Latvia on Friday night, the new Republic of Ireland manager said: "At the end of the day, it's hardly worth it.

“You would have to go and check, but I don’t think Sunderland would concur with his £40 million for a start. Even Sunderland wouldn’t do that.

“Seriously, one of those people he’s talking about [Steven Fletcher] actually, his goals helped Sunderland stay in the league, and Mignolet, they got £10 million for.

"I think they owe a debt of gratitude to [Ireland goalkeeping coach] old Séamus McDonagh, who was out there tonight, McDonagh who I think Simon Mignolet - who is playing brilliantly for Liverpool — would say he had a major influence in his career development."

Di Canio, who led Sunderland to Premier League survival last season before being sacked after five games of the current campaign, had told Sky Sports news on Friday morning: "I don't know if he knows the meaning of this word charlatan. Probably I can teach him, even if I am not English.

“I respect the opinion of manager Martin O’Neill but the fact that he spoke after six months, not straight away, that proves what kind of level he is. He is not very big.

“A charlatan is a manager who spends £40 million to be a top 10 club and then sees the club sink into the relegation zone.”

Di Canio stood by his claim that the Black Cats players were not in peak condition when he arrived on Wearside.

“The fitness levels were pathetic,” he said. “I had players who told me they had cramps from driving the car. I had three players with injuries in the calf after 20 minutes of a game. Six different players with problems means they were not fit.”

Di Canio was dismissed after a 3-0 defeat at West Brom, a result which was reportedly followed a day later by a training ground bust-up with senior players which led them to ask the board to take action.

Di Canio insisted, however, that no argument took place. “It never happened,” he said. “There was a typical meeting, as there was after every game to see the clips and analyse the game.

“Maybe there was opinion but this happens in every good family.”