The 62-year-old believes that either side could triumph during Tuesday's Clasico at Camp Nou, and is refusing to class 2012-13 as a failure for Spanish football
The two teams recorded a few in the first leg of their quarter-final in January, and will go head to head for a place in the last four at Camp Nou.
"It's a great advert for Spanish football. It's impossible to call," the Spain coach was quoted as saying by Sport.
Both sides recorded poor first-leg results in the last 16 of the Champions League, but Del Bosque is refusing to class this season as a failure for Spanish football until the campaign's end.
"Spanish football has been the best in recent years. We will have to wait until the second half of the season ends before reviewing it."
Barcelona and Real Madrid kick off at 21:00CET on Tuesday, and also clash in La Liga on Saturday.