Casillas: Defence will be difficult
Vicente del Bosque's side play their first warm-up friendly ahead of the tournament in Poland and Ukraine against Serbia on Sunday, but their preparation has been far from ideal as the scheduling of the Copa del Rey final means that no Barcelona or Athletic Bilbao players will join up with the squad until early next week.
However, Casillas is sure that if La Roja maintain their ambition and desire, they can once again conquer Europe. He told AS: "The other countries already know how we play, they don't need to study us. They are playing against the champions and they will be in top form to make the game their own.
"The national team, though, has more than enough in our play. The main rival will be ourselves for the effort, the desire and the attitude that we have to win it.
"We have the experience of winning the EUROs and the World Cup and we have to take advantage of this, although it will be very difficult to defend our title as champions of Europe."
Villa has been Spain's top scorer for the past three major tournaments but has not played since breaking his tibia in December, while Puyol has recently undergone surgery to resolve a knee problem, and Casillas knows how significant their absence could be.
"The injuries to 'Puyi' and 'El Guaje' [Villa] have been a hard blow, but this team has the players capable of occupying these positions and they can deputise," he said. "However, the feeling is that these are two very important injuries."