The former FIFA World Player of the Year has had a difficult season, playing just seven full matches in La Liga, but Rijkaard insists he still has faith in him.
"Above all I consider him a great person with a great character," he told Spanish sports daily AS.
"And more than his football qualities he has given a lot to his team-mates, to the club and to the fans.
"I don't want to say that there's a relationship, but after so many years working together I hold him dear and I always want well for him.
"I respect him a lot."
The 27-year-old attacking midfielder sat out Barca's 4-1 victory over Valladolid on Sunday, and was also absent for the Copa del Rey defeat at Valencia in mid-week and the 2-2 draw in Almeria last weekend.
He was sent for scans after complaining of a pain in his left thigh, but the club released a statement saying that no injury could be found.
Rijkaard, however, refused to criticise his player.
"The player has some pains and we hope that he will recover as soon as possible," the Dutchman said.
"We have to believe the player. Ronaldinho has given a lot to Barca."
