The Portuguese winger, who launched his autobiography last week, feels the departure of Jose Mourinho will be a major blow for Chelsea to overcome.
Ronaldo told the Sunday Mirror: "We were under more pressure last year because we had not won the championship for a few years, but there is always pressure to win with Manchester United. I believe we are going to win the League, the Champions League - or both."
"Chelsea will miss Mourinho because he is a great manager.
"I know we are not playing the best football at the moment, but I think our top form is coming."