Jose Mourinho has told the Sunday Times that Manchester United failed to evolve under his predecessors David Moyes and Louis van Gaal, describing their tenures as an "empty period" for the club.
United have struggled to replicate the success that saw them become the major force in the Premier League under Six Alex Ferguson, who guided the club to the last of their 20 top-flight titles in 2013.
Ferguson's successor Moyes was sacked after 10 months in charge while early promise under Van Gaal fizzled out, even though he ended his reign by winning the FA Cup.
Mourinho won two trophies in his maiden season at Old Trafford, including the Europa League which ensured United would play in the Champions League this term, but the former Porto, Chelsea and Real Madrid manager believes he inherited a side that were burdened by past successes.
He said: "There was an evolution in the other clubs; there was no evolution in this club. In all the areas that make a team successful I think we stopped in time.
"That was quite an empty period in the club with no evolution in areas that are important. It was the weight of the past on the shoulders of the players, managers, even boards, even probably owners, because when you are used to win and win and win, and suddenly you stop, it's like a heavy burden.
"Today, we have better working conditions, a better medical department, a better analysis department, a better scouting department, a better media department, and in many cases we did it without changing the people, which is quite important.''
Mourinho has added Romelu Lukaku and Nemanja Matic, two players he worked with at Chelsea, to his United squad this summer.
While Lukaku left Stamford Bridge for Everton early on in Mourinho's second spell in charge at Chelsea, the Portuguese said: "Lukaku was my player as a kid.
"He left [Chelsea] because he was thinking he deserves more opportunity, but he's such a good guy that during these years we were in close contact with a good relationship. So I knew he was an intelligent guy with a positive attitude.''
On Matic, Mourinho added: "I cannot say that I had better guys than him in my career.''