Martin O'Neill, the Republic of Ireland manager, has suggested that "burn out" may have played a part in Roy Keane's decision to step down as the assistant manager at Aston Villa.

The 43-year-old walked away from the Birmingham club yesterday, just 24 hours before they take on Burnley in the Barclays Premier League.

Keane - who also acts as assistant to O'Neill in the Ireland national team - intimated on his departure that he had struggled to strike a balance between the demands of his two coaching roles. The former Manchester United and Celtic midfielder had performed the dual role since July and O'Neill admitted that the responsibilities have likely taken a toll on his assistant.

"He didn't have any holiday - he went straight from international duty with us in America to the job at Aston Villa and eventually those things catch up with you, one side of Christmas or the other," said O'Neill, who is also a former manager of Villa.

"Roy being the perfectionist he is wanted to give everything to every single cause, but I think maybe a bit of family time now is perhaps something which is missing. We had a big discussion about the issue at the last international get-together. He was more concerned about having that full commitment to Villa and to ourselves.

"I said in the past and it's worth reiterating - I never had a problem with his commitment to the Republic of Ireland. Everything I was hoping he would bring to the table, commitment, enthusiasm, the strong desire we know he possesses, haven't been a problem. I am delighted Ireland has been his first choice."

Keane replaced Ian Culverhouse at Villa Park in the summer, with Lambert's former assistant leaving after being the subject of an internal club investigation. The Irishman departs with Villa just two points above the relegation zone, and with Lambert under increasing pressure from disillusioned supporters.

Villa are winless in their last eight games and head to Turf Moor today without key defenders Ron Vlaar, Philippe Senderos and Nathan Baker, while Christian Benteke is still suspended. Fabian Delph is also absent through injury.

That injury was once irksome to Keane, as was the problem endured by James McCarthy during the last international break. The Ireland midfielder pulled out of the squad ahead of a qualifying match with Scotland earlier this month, causing Keane to question the training and treatment methods of Everton.

Such aspersions were dismissed immediately by Roberto Martinez but the Everton manager is still determined to get to the bottom of the hamstring problems which have been afflicting his player. McCarthy limped off after only half an hour of a Europa League match against Wolfsburg on Thursday and is unlikely to feature against Tottenham Hotspur in their league match tomorrow afternoon.

"We're going to get him checked today. The reaction was good from last night but we'll find out exactly what the extent is," said the Everton manager, who acknowledged that Scotland striker Steven Naismith has also had hamstring issues of late.

"It's the hamstring that he had a bit of trouble with beforehand and we need to assess it with a lot of intention. It's a serious problem because it's a problem he's had before and we need to make sure we find the root of the problem.

"I would have had regrets if the injury had happened in the 80th minute, because clearly then it's because the tissues were fatigued and you're running a bigger risk. Football is a contact sport and you always run the risk of injuries. Yesterday was different. It was after 10/15 minutes, the soft tissues should have been in good condition. If you could predict what could happen, obviously you would stop those sort of incidents."