Real Madrid manager Carlo Ancelotti believes it will be difficult for Louis van Gaal to deliver instant success at Manchester United.
Following the club's worst ever season in the Premier League era van Gaal was named the new man in charge Old Trafford following David Moyes' disastrous reign.
United finished in seventh place and subsequently missed out on Champions League qualification last term and van Gaal's priority next season will be to ensure the club regain their place amongst the league's elite.
But Ancelotti, who won the Premier League and FA Cup double during his first season in charge at Chelsea in 2010, has warned it will be extremely hard for the former Barcelona and Bayern Munich coach to deliver the club's 21st league title at the first time of asking.
"They signed really good players this year but to build a team is not easy," Ancelotti told a press conference. "The Premier League is a very competitive league and it will not be easy to win it in the first year because there are a lot of teams who are really competitive and they want to win."
Ancelotti will test his wits against the former Netherlands boss when United and Real Madrid clash in the International Champions Cup in Michigan on Saturday as Van Gaal looks to extend the club's unbeaten run in their pre-season tour of the US.
Despite the friendly nature of the contest, 109,000 people are expected to be in attendance at the Michigan Stadium on the outskirts of Detroit and Ancelotti is expecting a tough test ahead of his side's UEFA Super Cup clash with Sevilla on 12 August.
"It is never a friendly with Manchester United," Ancelotti added. "We are happy and honoured to play. It's the last game of our tour.
"We want to go finish well and go back to prepare for the Super Cup. We need to play a good game on Saturday because we are playing a really fantastic team."