Sir Alex Ferguson believes Pep Guardiola will struggle to replicate the success he had at Barcelona when he takes charge of Manchester City.
The current Bayern Munich head coach, who won 14 major honours in four seasons at the Camp Nou, is set to replace Manuel Pellegrini at the Etihad Stadium at the end of the season.
The former Manchester United manager admits Guardiola's appointment is a coup for his former cross-city rivals, with the Spaniard's tenacious work ethic, coaching ability and trademark style of play revered across Europe.
However, speaking exclusively to Sky Sports, Ferguson fears the demands of Premier League football may stifle Guardiola's influence.
"Without question Pep has got a fantastic work ethic about him, he demands that from all of his training sessions," he said.
"Anyone who thinks they're not going to work hard at City won't last long. He has got great coaching ability, there is no doubt about that.
"Man City have made a real coup in getting him but Pep won't find it easy, English football is not easy.
"Every foreign coach that has come to England will tell you that. Arsene Wenger was talking about that a few months after coming and even Jose Mourinho was.
"Pep will be a success but I don't think he'll ever replicate what he did at Barcelona because that was a high standard - they were the best."
This season's Premier League campaign has seen the established clubs' dominance challenged like never before, with Leicester City and Tottenham's surprise emergence as genuine title contenders.
Ferguson expects a reaction from the so called 'big clubs' next season, just as he managed to do in response to successful campaigns from Blackburn, Arsenal, Chelsea and City during his tenure at Old Trafford.
And it is for that reason Ferguson feels Guardiola is not guaranteed immediate success at Eastlands.
Pep won’t find it easy, English football is not easy. There is no guarantee Man City can win the league. That’s the beauty of the Premier League.
"You have to ask what the big clubs are going to do," he added.
"If you take my time at United, when Chelsea and Jose came on the scene, in the first two years they had quick starts, so I had to accept that challenge.
"That's what you have to do when you're a big club. Arsenal, Liverpool and the other clubs have to accept the challenge when they are not good enough.
"They'll have their own ambitions and will be desperate to win the league next season as much as City, so Pep there is not a guarantee they can win the league.
"That's the beauty of our league. Arsenal, City, Liverpool, Chelsea, Tottenham will want to do something and now, of course, Leicester City are there. Who's to say they can't win it next season?"