Jose Mourinho says he brought on Marouane Fellaini to counter Everton's direct style in the closing stages of their match at Goodison Park.
Fellaini came on against his former side in place of Henrikh Mkhitaryan in the 85th minute for his 100th United appearance since joining in 2013.
But it was a landmark outing to forget for the Belgium international, who promptly fouled Idrissa Gueye in the penalty area, with Leighton Baines scoring the resulting penalty as Everton claimed a 1-1 draw.
United therefore failed to preserve the lead given to them by Zlatan Ibrahimovic, but Mourinho explained he was trying to ensure his side did hold out to secure all three points in bringing on Fellaini.
"I thought you would know more about football than you do because the answer is obvious," Mourinho told reporters when asked why he had made the substitution.
"Everton do not play beautiful football anymore. They are now direct. Their style is direct. [Ashley] Williams is direct. Everything is direct.
"When they are losing they intensify their directness. When you have a player who is two metres tall [Fellaini], you bring him on to deal with that."
But when asked for his verdict about the penalty incident, Mourinho simply said: "I didn't see it."
Questioned about Marcos Rojo's two-footed first-half challenge on Gueye, he also replied: "I didn't see it."
United are back in action against Zorya in the Europa League on Thursday, before they host Tottenham in the Premier League on December 11.
