Brazil's opening World Cup match against Croatia is just over 100 days away but the stadium set to host the showpiece opening match may not be ready until less than four weeks before the start of the tournament, according to Fifa secretary general Jerome Valcke.

In a worrying bulletin released yesterday, Valcke said that work on the stadium in Sao Paulo may now not be completed until mid-May, which will raise major concerns around the world about Brazil's ability to successfully host the biggest football tournament in the world.

"There are no more deadlines," said Valcke.

"We are just over 100 days from the first game in Sao Paulo, which is not ready and will not be ready until May 15 and we have other stadia which are not ready either."

One of those stadiums is Curitiba, which has also been hit by problems and is due to host Nigeria's opening game against Iran on June 16.

Valcke, who has been travelling to and from Brazil in his unofficial role as chief spokesman for the tournament, was at pains to try to add a positive note to an issue that is gaining worrying momentum.

"The goal is that on June 12 until July 13 everything will be working," said Valcke.

"It's true whenever you receive something late it's a challenge to make sure it is ready on time.

"It's a bit last-minute but it will work in the end. For example, we still have to install all the IT solutions for the media.

"Without IT and without the telecommunications in place in the stadia you will say we are the worst organisers and it was the worst event.

"But to install the IT in a stadium needs at least 90 days and we have to work for all the other people who also have their interests such as our commercial partners, our media partners, hospitality and so on.

"We are having to work in situations where the cement is not even dry.

"But it will work in the end and you will have what you expect and the teams will have the best conditions because the stadia are the best."

This latest update came just a day after parts from the roof of the Mineirao Stadium in the city of Belo Horizonte - which will host one of the World Cup semi-finals - fell onto the pitch during a storm just hours before a regional championship match between Cruzeiro's and Minas Boca.

No-one was injured.