"The best thing to take on Spain would be to allow us to play with 22 players instead of 11," Valdes said in Spanish sports daily Marca.
"Against Spain it is absurd to think of it as just another day and just another team.
"You can't take them head on. Everything we try to do in games will have to doubled. Twice the attention, the concentration, the effort, helping each other out and so on."
Visitors Spain are the world and European champions. They top the FIFA world rankings and last lost a match in a 1-0 friendly reverse in England a year ago. Since then have won Euro 2012 and they top their group in qualifying for the 2014 World Cup in Brazil.
Panama are ranked 46th in the world but have reached the final stage of the CONCACAF World Cup qualifying competition. They will host a Spain side lacking many of their regulars.
Vicente del Bosque has rested stalwarts such as Xavi, Xabi Alonso, Gerard Pique and Fernando Torres, giving a number of fringe players the chance to impress.
Chelsea's Juan Mata, who was left out of the last three Spain squads, is back in the side and had words of praise for Panama coach Valdes.
"Dely Valdes played for Real Oviedo," Mata told a news conference, referring to the Spanish club where he started his playing career.
"I have seen goals he scored in their Tartiere stadium. He is the image of football in this country and I am sure he will imbue his team with the same footballing spirit he had."