Manufacturers adidas claim that altitude is the main factor affecting the World Cup ball - not its design - as criticism from players grows.

Slovenia's Robert Koren admitted that his winning goal against Algeria was helped by the Jabulani ball, which he said was "really difficult to control".

Nigeria's Dickson Etuhu told the BBC he thought it was "the worst ball ever".

An adidas spokesman said those who have had the most problems are nations who have not practised enough with it.

"What is strange is that people are saying the ball is lighter and that is just not true," said Thomas Schaikvan, head of global public relations at adidas.

"Playing at altitude is not the same as playing at sea level - that is just plain science. "There are players who play in leagues with other balls, there are players that have not played in the Africa Cup of Nations, and players with other federations who have not practised with this ball.

"Those are the players who take the most amount of time to get used to it."

The Jabulani was supplied to all countries in February but the issue of practising with it over a concerted a period of time, either within competitive games in domestic leagues or when training with club or national sides, appears to be tied up with sponsorship.

The new Jabulani ball has been extensively used in Germany's Bundesliga as well as France and Argentina - all national sides sponsored by adidas - and a number of other national leagues.

Germany romped to a 4-0 win over Australia in their opening group D encounter on Sunday.

The Jabulani has also been used in Major League Soccer in the United States, who held England to a 1-1 draw on Saturday with goalkeeper Robert Green believing his error in allowing American forward Clint Dempsey's shot to squirm from his grasp was partly because of the movement of the ball.Koren also agreed with that observation, while Algeria's Madjid Bougherra called the Jabulani "horrible" after the glaring mistake made by their goalkeeper Faouzi Chaouchi when he allowed the Slovenian's shot to bounce past him in their 1-0 group C defeat.

When BBC Sport asked the English Premier League if the adidas Jabulani had been considered for use in its matches ahead of the World Cup, a spokesman said: "We use Nike balls.

"We've had a contract with them for nine years and just signed a new three-year deal with them."

After Nigeria's 1-0 defeat by Argentina, Etuhu said: "You can't head it [from goalkeeper's kicks]. You don't know where it's going to go. If you pass the ball into a player's feet, if it's off the ground - you don't know where its going to go.

"It's the worst thing they could have done. It's so hard to play with."

The Jabulani - from the Zulu word "to celebrate" - came in for heavy criticism from goalkeepers prior to the start of the tournament.

England's David James joined Australia's Mark Schwarzer, Italy's Gianluigi Buffon and Iker Casillas of Spain in castigating it.

"The ball is dreadful. It's horrible, but it's horrible for everyone," said James.

"There will undoubtedly be goals scored in this tournament which in previous tournaments with different balls wouldn't have been scored. It will allow extra goals, but leave some goalkeepers looking daft."

Buffon added: "The trajectory is really unpredictable. Usually you get used to it, but in this case every touch comes with the unknown."I noticed the first day that this Jabulani ball wasn't right. The World Cup brings together the best players in the world and to those players you must provide something decent. The new ball is not decent."

In December 2006, NBA commissioner David Stern authorised a switch back to old leather basketballs after controversial new synthetic balls were roundly criticised by discontented players after three months of use.

"Our players' response to this particular composite ball has been consistently negative and we are acting accordingly," said Stern in a statement at the time.

"Although testing [by Spalding] demonstrated the new composite basketball was more consistent than leather and statistically there has been an improvement in shooting, scoring and ball-related turnovers, the most important statistic is the view of our players."

Fifa has not made a comment on criticism of the Jabulani ball.