The 22-year-old has two more games to serve of his suspension for aiming a headbutt at Richard Hughes during Manchester United's 1-1 draw at Pompey last week.
Manager Sir Alex Ferguson believes the Portugal winger only had himself to blame after falling for what he described as Pompey's "intimidation tactics".
However, Ronaldo is unrepentant.
He told the Daily Mirror: "I am frustrated because three matches is unjust.
"I am willing to resist the provocation - but only up to a limit.
"That limit was passed at Portsmouth. It was just absurd."