Rijkaard substituted the Brazilian in last week's goalless draw with Osasuna and withdrew the player again in Wednesday's 3-0 Champions League win over Lyon.
"I believe Ronaldinho is capable of doing the things he has done in previous years," he said.
"I think we can get him back (to his best). It's all about action-reaction and sometimes that implies a bit of suffering, but when he reacts he is a phenomenal player.
"There is no doubting the quality he has, but he must react and demonstrate that quality."
Rijkaard maintained that Ronaldinho is a "very, very important player for the squad", but defended his decision to substitute the South American.
"He is one of the best players in the world and he has shown that, but sometimes a change is necessary to add new life to the team," he said.