By Mandeep Sanghera
BBC Sport in Berlin
Croatia centre-back Robert Kovac says he was bewildered at the lack of threat posed by Brazil striker Ronaldo.
Ronaldo failed to trouble the Croatian defenders on Tuesday
The holders won 1-0, but 29-year-old Ronaldo was anonymous and was substituted after 69 minutes.
"I don't know what happened to him," Kovac told BBC Sport. "He didn't run and stayed in front of us. He must be tired. He hardly touched the ball.
"It was very easy. I've played against him before and it was very difficult. I don't know what's happened with him."
Ronaldo entered the competition on the back of a troubled season at Real Madrid with criticism being levelled at him for being overweight.
He seemed to run faster when he was taken off against Croatia than for most of an outing which saw him have just one noteworthy shot.
The performance even surprised the Croatia bench, with second-choice keeper Joe Didulica saying: "I would love to see the statistics of how far he ran.
"I think he made three or four sprints of 10 metres or so. I was amazed looking on from the bench."
Ronaldo has said he has not reached his ideal level of fitness
But Croatia defender Josip Simunic offered some support for the man who scored 12 goals in three previous World Cups.
"Ronaldo is the most dangerous player in the world," said Simunic.
"I don't know what everyone is talking about and I am 100% sure he will score four or five goals in the tournament. Just wait and see."
Brazil coach Carlos Alberto Parreira and Tuesday's match-winner, Kaka, were both quick to jump to Ronaldo's defence.
Parreira admitted the player was "lacking a little bit of sharpness" but that he would still start their second game against Australia on Sunday.
"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," he said.
And Kaka 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."
The Brazilian newspapers were less supportive of Ronaldo, who to date has 12 World Cup goals under his belt.
Former World Cup winner Tostao, writing for the Folha de Sao Paulo newspaper, described him as "slow and weird."