Erik ten Hag has said that it is difficult to effectively integrate new signings into his team so early in the season following his side's 3-0 defeat to Liverpool at Old Trafford on Sunday, adding: "I'm not Harry Potter."
During a fierce defence of his record in what was at times a tense news conference after the game, the Dutchman assured fans his team "will be fine" and have a "big chance" to lift another trophy at the end of the campaign.
"It's just the third game in the season, we have to build a new team," Ten Hag said.
"I explained this so many times. We will build it. We have young players and players to build in. Today we had three players who started for the first time this season. We will be fine. It is clear we have to improve but at the end of the season I am confident we will have a big chance to lift another trophy."
Ten Hag was forced to substitute Casemiro at half-time after the Brazilian made two errors leading to goals for Luis Díaz.
New £50 million ($65.6m) signing Manuel Ugarte was watching from the stands after being presented on the pitch before kick-off and Ten Hag admitted the Uruguayan will need time to get up to speed.
"So this is another one, we have to build him into the team," he said.
"It will take time, so it's not like I'm Harry Potter. That is what you have to acknowledge. And if you see Manuel Ugarte, he didn't play so far in the season. Not one match minute. He needs to build his fitness and then we have to build him in the team."
A defiant Ten Hag also went on to reject a suggestion that his team continue to be punished for familiar mistakes.
"Maybe you can explain to me which mistakes," he replied.
"You are sure? I don't think so, otherwise you wouldn't win trophies as we have. I am sorry for you. I think we won after [Manchester] City the most trophies in English football in the last two years, so I am sorry for you.
"There are [positives] but I don't want to talk about this. It hurts, it hurts especially for our fans, we have to be humble and move on."