Brazil coach Carlos Alberto Parreira insists he will stick by Ronaldo and give him the chance to regain some sharpness when the defending champions face Australia on Sunday.
Brazil were unconvincing despite a winning start to the defence of their trophy, and Ronaldo in particular was virtually static.
Parreira said: "Ronaldo has not been playing for the last two months and has had only two friendlies so it was natural he felt a bit heavy as it was very hot, but I'm sure he will improve as the tournament goes on.
"Ronaldo will start against Australia because he needs to gain pace, and he is a decisive player.
"Australia are physically strong with three or four very good players from the European leagues - (Harry) Kewell, (Marco) Bresciano and (Tim) Cahill especially.
"Our business is to put the ball on the pitch and use our technical capabilities - we are not going to fight it out.
"That game is decisive for whoever wins it has qualified for the last 16 and that's our initial objective."
Victory was achieved courtesy of a brilliant goal by Kaka but the South Americans only played well in flashes.
Speaking after the game the goalscorer said: "It was essential to win our first match but we all have to improve and that includes myself.
"We have to improve our movement, to be more creative and to mark better. I'm sure the next game will be better as we will not feel under so much pressure."
Kaka admitted that 29-year-old Ronaldo's lack of mobility is something the Real Madrid player will need to change.
He added: "Ronaldo has said he has not reached his ideal level of fitness so let's wait until he improves his performance and is the Ronaldo that we know and like, but yes a little more movement from him would be ideal."
Croatia's coach Zlatko Kranjcar claimed his side had outplayed Brazil for much of the game and in particular praised Rangers striker Dado Prso whose physical presence was a constant threat.
"I didn't think we deserved to lose because for most of the time we were the better team and it's a pity we didn't make better use of our opportunity," Kranjcar said.
"If you make only one mistake against Brazil you will usually lose but it show that we are well prepared for the next two matches.
"Prso played very well in attack and he had some chances to score. We showed our strength and I'm convinced we will use that in the games to come."
Influential skipper Niko Kovac went off with bruised ribs and Croatia will have to wait and see whether he will be ready to play the remaining group games.