The inaugural event in the Spanish port city, with an attendance capacity of 112,000, was nearly sold out last year.
But with only one month to go until the 2009 edition, chief organizer Carlos Garcia revealed that ticket sales this time are not going well.
"It is not the best situation. We are content with the rhythm of sales and hope to reach 80 or 90 per cent, although at the moment we have about 30,000 sold," he said.
"We must not forget that many tickets are sold abroad and many bookings are made by internet at the last moment," Garcia added.