Johannesburg - FIFA has finally acknowledged that there may be something wrong with the Jabulani World Cup ball, but won't act on the problem until after the tournament.

Many players have likened the Jabulani to a "supermarket ball," saying it is too unpredictable and flies through the air too easily.

"We're not deaf," FIFA secretary general Jerome Valcke said Saturday at a news conference. "FIFA is not unreceptive about what has been said about the ball."

Valcke said that FIFA will discuss the matter with coaches and teams after the World Cup, then meet with manufacturer Adidas.

"There are rules for size and weight. ... But the ball has to be perfect," he added.

Goalkeepers have complained about the ball at every recent World Cup, although this time forwards and even coaches have added their laments.

Brazil manager Dunga got into a verbal spat with Valcke over the Jabulani before the tournament, challenging the FIFA executive to come out onto the pitch and attempt controlling it.

Denmark defender Daniel Agger said the ball made some outfielders look like "drunken sailors."

The Jabulani could create even more problems in the knockout phase beginning Saturday, since games could be decided by penalty shootouts.

"The balls have changed over the last couple of years, they have become a lot faster and in addition to that in Johannesburg we are playing at an altitude of 1,700 meters, which makes the ball even faster," former Germany goalkeeper Oliver Kahn said. "Thus the goalkeepers work even harder, but I don't think that we can take the ball or the altitude as excuses.

Adidas has made the World Cup ball since 1970 and is contracted through 2014. The German company has defended the Jabulani, saying it doesn't know what the fuss is about because all the qualified teams were given the ball before the tournament to test it.

"There's a lot of talk about stadiums, infrastructure and TV and that's nice and all, but first we've got to worry about balls, spikes and jerseys," Italy goalkeeper Gianluigi Buffon said. "I don't see why we can't just go back to the old black-and-white chequered version we all played with as kids."

As for the aesthetics, Valcke said that the ball had been criticized in the past as too colourful, and that's why this version is whiter.

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