Jose Mourinho has said he stopped Romelu Lukaku from taking a penalty against Benfica in the Champions League on Tuesday to "protect" him.
Mourinho said the striker would only be allowed to take another penalty when there was nothing riding on the kick after he missed from the spot against Leicester earlier in the season.
The manager ordered Daley Blind to take the second-half penalty against Benfica after Lukaku had initially stepped up, with Blind converting to seal a 2-0 win.
It would have been a chance for Lukaku to break a goalless run that stretches back to Sept. 30, but Mourinho told Viasport Fotball: "I'm the manager and I make the decisions and he missed the last one.
"I want him to take a penalty when there is no pressure, there is no responsibility and there is no need to score the goal.
"We are playing in the Champions League, we need points -- even with 12 points we are not even qualified.
"It is an important moment in the game, 1-0, with 10 or 12 minutes to go, I want a player free of the pressure of missing the last one."
Mourinho said he was "really happy with his personality, really happy that he wants to take the responsibility, but I'm here to sometimes to protect the players and protect the team."
He said that he had needed "to protect him because he missed the last one."
And he added: "I think I protect him because if he misses the penalty the team would be in the danger of a 1-0 result. It would be second consecutive miss for him.
"He will take a penalty when the game is over, and the game was not over."
Lukaku began his United career with 11 goals in 10 games following his £75 million summer move from Everton, but he has now failed to score in six games.
He started the season as United's designated penalty-taker but missed in the 2-0 win over the Foxes at Old Trafford in August.