Roy Keane says Irish and Scottish players must improve their lifestyles if they are to match the fitness levels of football's top nations.

Keane won 66 Republic of Ireland caps and played in Scotland with Celtic.

"The English lads don't seem to be too bad," said the Sunderland boss. "The French and Spanish are good.

"But the players with the biggest problem in terms of changing their mentality are certainly the Irish and the Scottish players."

The former Manchester United midfielder's comments come after Northern Ireland boss Nigel Worthington expressed concern at the fitness levels of members of his squad who are struggling to get regular first-team football at club level.

"They have got to go back to their clubs and do extra work because they are not fit enough," said Worthington following his side's 2-0 friendly defeat by Hungary on Wednesday.

And Keane insists a healthy approach to life away from football is crucial to success on the park.

"I was brought up eating rubbish, drinking rubbish, so it is trying to change that mentality," added Keane.

"You have to try to remind the players and provide these dieticians and speak to the players and eventually, you hope the penny will drop.

"You hope - sometimes it doesn't.

"I will go back to the game a few weeks ago, the United and Arsenal game.

"You have got to be able to sprint to people, you have got to play for 90 minutes.

"You can't be tiring after 45, 50 minutes, not in the Premier League. You can't do it."

The current Sunderland squad features several Republic of Ireland internationals as well as Scotland first-choice goalkeeper Craig Gordon and Northern Ireland regulars David Healy and George McCartney.

And though the Black Cats have worked hard on educating their whole squad, Keane says the ultimate responsibility lies with the players.

"You can provide everything for them in terms of fitness coaches, the right foods, the right hotels or whatever it might be," Keane said.

"But of course, you cannot follow players, you cannot follow players when they leave your training ground.

"I think a lot of players in the Premier League can be fitter. A lot of players have the excuse that they are not playing - yeah, but you can still get fitter, you can still do extra, still do swimming, still do more weights, get your body-fat down.

"I did it both ways. I was able to get away with it when I was younger, having high body-fat and not leading the right lifestyle.

"But the last six, seven, eight years of my career, you certainly wanted to be as fit as you possibly could.

"It's up to yourself. Nobody should really throw that at you if you are a professional sportsperson, that you are not fit enough."