Zidane, an advisor to Real Madrid president Florentino Perez, said the criticism was ill-founded and that Spain, who topped Group C after coming through it unbeaten, remained favourites going into Sunday's quarterfinal with France.
Del Bosque's tactic of not starting with a recognised striker, which he did in the opening 1-1 draw with Italy, has attracted criticism in some quarters but Zidane, who turns 40 on Saturday, was having none of it.
"One hears a lot said that Spain are not playing well or that they are playing without a straight No 9 or any other number of things, but they know very well where they are going and where they want to go," Zidane told Spanish radio station Cope.
Zidane, who played under del Bosque at Real Madrid and scored a stunning goal in their Champions League final win over Bayer Leverkusen in 2002, said the world champions were clear favourites for the game.
France slipped up in their final match losing 2-0 to already eliminated Sweden which saw them end up second in the group to England and the intimidating prospect of playing the Spanish.
"For me, the favourite is Spain, but at the same time, a one-off match such as this anything can happen, that is the beauty of football," said Zidane, who defied Spanish media predictions of being sent into early retirement by Spain in the 2006 World Cup quarterfinals by scoring in the 3-1 victory over them.
"We all known that Spain are the favourites, not just for this match, but also for the Euro."
Zidane, a Euro winner in 2000 having won the World Cup in 1998, said he believed the outcome of the match would be decided in midfield.
"Spain will look to have the most possession, it is their style of play and they do it well," he said.
"The French know this. Thus it will be in midfield where it will be decided."
Zidane took the Spanish media to task for their criticism of the Spaniards.
"I think that you (the Spanish press) have been hard on Spain. They are not playing as badly as that. Of course they could play better, but they have played opponents who are good and wanted to win."
Indeed Zidane harking back to the victory over Spain at the 2006 World Cup said the Spanish media could have played a role in motivating him and his teammates.
"Spain is a lot stronger today. Maybe in 2006, we were stung by what the Spanish media said about us ('the old French'). We wanted to prove that we could beat them."