Mourinho has been widely criticised for lashing out and pointing fingers at his players during the Red Devils' recent slump in form, but Deco feels his former coach is justified.
"If you are playing at a club like Chelsea, United, Barcelona, Madrid - the big clubs - you need to be prepared to do your best. If you want to play at a high level you need to be able deal with everything," the ex-Chelsea playmaker told reporters.
"I don't like the coach criticising me, but he knows better than us players and sometimes he does that not to pressure players but to give something different.
"He knows better than us, he's with them every day and of course the players don't like it but sometimes it works.
"At Porto sometimes publicly he did the same thing. It is part of his work, he knows sometimes the player reactions will be different," the 39-year-old added. "When you lose and when you are not playing very well you need to improve.
"Whether the coach says it on the media or in the dressing room it is the same thing, when the team is not playing well everyone knows that they need to do better.
"Maybe Jose knows that when they have lost a few games they need to improve. I don't think it's a problem."
