MANCHESTER, England — Jose Mourinho does not doubt that Henrikh Mkhitaryan will be a success at Manchester United.

It just might take some time.

Mkhitaryan, a $33.5 million signing from Borussia Dortmund in July, has not played for United since being substituted at halftime in the 2-1 loss to Manchester City in the Premier League on Sept. 10. He sustained a minor injury on international duty with Armenia in early October but hasn't even been in United's 18-man squad for recent games.

That's some fall in status for a playmaker who had 23 goals and 32 assists for Dortmund last season, was the German league's player of the year, and was widely touted as one of the shrewdest Premier League signings of the off-season.

Mourinho said Friday that Mkhitaryan is not injured, and was just struggling to adjust to the English game.

"Some players find it very easy, whereas others need more time. They need time to feel the intensity, the aggression, the game without the ball and the competitiveness," Mourinho said.

"The realities are often different, particularly in terms of the competitiveness. It doesn't matter who you are against, you have to play at the highest level otherwise you will not be able to do it. Micki needs time to become the top player he knows he can be."

That is nothing new to Mourinho.

He said the same happened with Willian at Chelsea and Angel Di Maria at Real Madrid, in Mourinho's two previous coaching jobs.

"It happens with defenders, but it is often easier for them to adapt than attackers," Mourinho said. "In Micki's case, the process was interrupted by injury, which does not help ... Being out for a month meant he has had to go through the process of getting match-fit, then once he has that he needs the competitive level to do it. We believe him and, sooner or later, there will be no problem."

Before that first start for United in the derby, Mkhitaryan appeared three times as a second-half substitute.