A senior Spanish government official on Tuesday asked the organisers of the Madrid Masters tennis tournament to stop using models as ball-girls, saying it was sexist.

Top player Andre Agassi also weighed in on the controversial decision to swap volunteer young fans for the 19 to 28-year-old professionals, saying he was not convinced it was the way to promote tennis.

The models needed two weeks of training for their tasks of picking up stray balls and handing towels to players. They will work most of the televised matches at the week-long tournament.

Secretary for Equality, Soledad Murillo, has sent a protest letter to the tournament director, a major sponsor and the mayor of Madrid in which she says the spirit of the tournament is being undermined.

"Soledad Murillo ... considers that this move contributes to building a clearly discriminatory vision of women, as simple objects of decoration and entertainment," the Labour and Social Affairs Ministry, where Murillo works, said in a statement.

"Traditionally this work is done by the male and female students of tennis academies, which is an example of equal treatment ... that does not distort the real essence of sporting competition."

The arrival of the models, who wear skirts and tight tops emblazoned with the name of a sponsor, had already stirred up controversy over whether they were trivialising the game -- and might distract players.

"I think it is important for our sport to understand its product clearly, and I'm not quite convinced this is part of our product," Agassi told reporters after a match in which the umpire had to remind a confused ball-girl to return to the side of the net.

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"It was difficult, to say the least, to concentrate on the ball, but I suppose I had an advantage -- I'm used to playing with my wife (Steffi Graf)," he added.

In her letter, Murillo said she regretted that the sexist use of images of women was becoming more widespread. Many Spanish women still consider their society is macho.

"(Murillo) calls for this treatment, which has become customary in fashion and publicity, not to be transferred to the sporting arena," the statement said.

Tournament organisers were not immediately available to comment.