The Portugal international wasn't his usual enthusiastic self in Saturday's 0-0 draw with Chelsea.
And McClaren wants to see the playmaker remain positive even when things aren't going his way.
"He's disappointed because he's been taken out of the middle and he's out on the right-hand side.
"I saw it last week against Newcastle, when he went out wide, and I'm seeing it again now. His body language is not good, he's not getting involved.
"He needs to be in the game and on that right-hand side he's not moving from there, he's got to move from there, he's got to get his head up and get back into the game and affect the game.
"At the moment he's just standing out on the right and he's making it very easy for [ Chelsea left-back] Ben Chilwell."