Sir Alex Ferguson has warned Pep Guardiola that he will find it difficult to reproduce his success at Barcelona and Bayern Munich in the Premier League with Manchester City. City announced last month that Guardiola would take over from Manuel Pellegrini on a three-year deal in the summer, ending months of speculation over the Spaniard's future.
While heaping praise on the Bayern manager's work ethic and coaching skills, Ferguson cautioned that he could struggle to come to terms with the demands and unpredictability of English football.
"Without question Pep has got a fantastic work ethic about him, he demands that from all of his training sessions," the legendary Scot told Sky Sports. "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," Ferguson added. "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."
City face a fight to qualify for the Champions League next season after a dire run of results that has included just one win in six in the league.
The Etihad outfit are just one point ahead of arch rivals United in fourth place in the league table and are a mammoth 15 points behind leaders Leicester City.
Ferguson expects the Premier League's traditional big clubs to respond next season after being overshadowed by the likes of Leicester and Tottenham this campaign.
"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," the 74-year-old stated. "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 there is not a guarantee they can win the league."