Karim Benzema struck his 18th goal of the season for the 3-0 win.
"If Ronaldo leaves and there is no real top attacker in his place, you know that it will be a difficult year," Courtois said. "You take 50 goals away.
"You hope that Benzema or Bale will score more and partly they do that too. We are making progress in the last few weeks.
"We have won the Club World Cup, are still active in the Copa del Rey and the Champions League.
"Okay, in LaLiga we are 10 points behind. But sometimes Barcelona also has difficult matches that they win in the last minute.
"Maybe it's a bit of a transitional year. For me it does not matter much if the first year is less if the next ones are top."