Ronaldo is back to today's clash against Everton and Ferguson said: "It is possible some players might try it on with Cristiano.
"But it is up to him to control himself and go out there and show what a good player he is. He will only be helping the opposition by reacting. I just hope the referee is strong and senses the mood of the game."
Fergie will be relieved to have Ronaldo back as United had lost their spark in his absence.
The Scot said: "It is a big plus having Cristiano back.
"You miss players who can influence games and change their pattern. He creates opportunities and scores as we saw last year so he has been a miss."
Ronaldo, 22, has been kicking his heels during his suspension and is raring to return.
He said: "I hate being suspended because I grow bored when I cannot play.
"But sometimes, in the heat of the moment on the pitch, things happen and only a professional player can understand that."