The midfielder who amassed a total of 718 appearances for the club questioned the Portuguese manager's idea of a "new-look" for United, saying former manager Sir Alex Ferguson has already left the club with a flawless recipe for success.
United will head into the new Premier League campaign having failed to bring in a new centre-back, despite being frequently linked with the likes of Toby Alderweireld, Harry Maguire and Jerome Boateng.
Jose Mourinho selected a youthful squad to take to America after a number of players were missing due to the World Cup.
"The other clubs who compete with us are really strong and already have fantastic teams, or they are investing massively like Liverpool, who are buying everything and everybody", said Mourinho.
Jose Mourinho aims early dig at 'serial winners' Liverpool and Tottenham
Last season may have been their highest finish since Sir Alex Ferguson retired, but the 19-point gap to runaway Premier League champions Manchester City underlined the improvements required.
Paul Pogba did not follow suit as the French World Cup winner's frosty relationship with Mourinho has sparked interest from Barcelona.
Mourinho has made no secret of his disappointment that he was not able to significantly strengthen his team during the close-season. "I will see how available they feel they are and understand how they can help or not help". I had my plans for many months and I find myself with the market closed in a situation I did not think I would be in.
"Of course the boys with the proper pre-seasons, they were in much better condition", Mourinho said. "As a Man United fan, winning is the most important thing". I needed more changes, but I couldn't so it was not easy to manage the game from the touchline point of view. "I like challenges, I want to progress and win more trophies".
Although he waned towards the end of the game, Pogba took his penalty very well early on to put United 1-0 up and played a number of unsafe passes into United's forwards as the Red Devils looked to counter-attack in the second half.