Casillas: Limited preparation time no excuse
The world and European champions take on Serbia in Switzerland on Saturday after a provisional 21-man squad started their build-up this week without up to a dozen players from Chelsea, Barcelona and Athletic Bilbao.
"We'll see if it works against us or not at Euro 2012," the Real Madrid goalkeeper told a news conference at their training camp in Austria.
"If Spain don't do well someone will use it as an excuse. It's true, for us, it is a different squad get-together but this is not to say it is worse than previous ones.
"There is no need to dwell on it because all the members of the squad have known each other for a long time now."
Juan Mata and Fernando Torres join the squad this weekend but will not play against Serbia after helping Chelsea win the Champions League final against Bayern Munich last weekend.
Barca and Bilbao compete in the King's Cup final on Friday and Spain coach Vicente del Bosque will call up players from those teams when he names his final 23-man squad on Sunday for the tournament in Poland and Ukraine.
Del Bosque has two more friendlies, against South Korea in Switzerland on Wednesday and China back in Spain on June 3.
They start the defence of their European title against Group C rivals Italy on June 10 in Gdansk.