Jose Mourinho said he would not be rushing into judgement on his players as a result of Manchester United's 4-1 drubbing by Borussia Dortmund in Shanghai on Friday.

"Unfair to make any decision. Day by day they are starting to win my trust," Mourinho said of his players, who only returned to pre-season training 10 days ago.

Dortmund have been back for a month already, and it showed with superior levels of fitness in the International Champions Cup match played in an energy-sapping temperature of 35 Celsius despite an 8.05 pm kick-off.

"I know in pre-season the team in the advance stage of preparation looks better," he said.

"It happens year after year. It was too obvious. We knew after 10 minutes that one team started training a month ago and played four games."

Gonzalo Castro scored twice for the German side, Pierre-Emerick Aubameyang bagged a penalty and Ousmane Dembele showed why the Frenchman is regarded as one of the best young talents in Europe with a superb finish.

"The reality is even in this situation we have six players still in Europe, plus (Wayne) Rooney and (Chris) Smalling who are only training. That is eight not involved.

"We had no (Zlatan) Ibrahimovic, (Anthony) Martial, (Marouane) Fellaini, (Morgan) Schneiderlin - lots of them aren't here yet."

It was Mourinho's first defeat as United manager in just his second match, after a 2-0 win at Wigan last Saturday.

The Portuguese former Chelsea and Real Madrid boss reiterated his pre-match comments that he needed one more signing to get the balance of his side right.

"Our fundamental market is 75 percent done and when we sign one midfield player, that will be done," he said. "The fundamental market is four players and we just need that crucial one."

Mourinho's opposite number Thomas Tuchel has been busy in the transfer market in the past two days with the return to the club of World Cup-winning goalscorer Mario Goetze and Germany's former Chelsea star Andre Schurrle.

"I am very happy that the transfer (of Goetze) worked out. By making this decision and committing, Mario has chosen to take the difficult path," said Tuchel, referring to the 24-year-old striker angering Dortmund's fans by leaving for Bayern Munich two years ago.

The German also praised Schurrle as an unselfish player who would help the balance of his side.

"We urgently needed a player up front. He has special qualities. He puts his ego aside," said Tuchel.

"We define our style as attacking when we have the ball, and attacking the ball when we are defending. He can do that."