Campbell has pace and a body-feint trick, but not enough vision to thread the ball into the net consistently as it requires games and experience for it. I repeat: the Premiership is not a training ground. How many times can you allow a young player to make mistakes?
Ronaldo's dribbling is part step-over, part pace, not orthodox like Messi, who can negotiate out of tight, tricky space around him. You can mark Ronaldo out of the game by allowing a pacy defender to study his movement, and doubled-team on him if necessary. Ronald is most dangerous when coming in from deep. Remember the game against Fulham when opponents were unable to mark him in a sea of players as he came from now where - cue Roma - and his vision allowed him to let fly a ball into the net. Wonder how he has got his vision, may be from Boring's 101 theory book.
Saha has said he even tried alternative medicine too, and now what? Four major competitions with two strikers on the duty roster? Remember mental fatigue syndrome means a loss of form.
His best role is as an auxiliary striker, or coming from deep, just like Scholes in the old days. See above.