The Spain coach's number two disclosed that there a still a few places in the team's starting XI that are yet to be decided ahead of Euro 2012
La Furia Roja are unable to call upon two of players who helped lead the team to the title in 2008, with Carles Puyol and David Villa missing the tournament through injury.
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The Barcelona duo would have played key roles in the competition, and Grande admitted to Radio Marca that there are "a couple of doubts" over who would line up against Cesare Prandelli's men in Gdansk.
The 64-year-old went on to warn his players that their status as favourites is by no means a guarantee to success, and highlighted the importance of Andres Iniesta to Spain's chances of continental glory.
"We are on a phenomenal streak, we have a great group and we are optimistic. We are favorites, but favorites also fall," continued.
"He [Iniesta] is a vital player for the team."
Spain begin their Euro 2012 campaign against the Azzurri on Sunday June 10, and will also have to deal with Croatia and Republic of Ireland in the group stage.