The Manchester United midfielder has admitted Scotland face a tough task against the World Champions.
“You are talking about the European and world champions and I think nobody can argue with the football they play,” said Fletcher.
“I think arguably they will go down as one of the greatest teams of all time not only because of what they have won, but because of the way they have played, they have played the game passing the ball, keeping possession off teams and outclassing everyone really over the last couple of years.
“So I think the manager is probably right we, are coming up against a top class side.
“We have played against good teams in the past, France and Italy, but I think this Spanish team might have a slight edge over those.”
He added: “It is a challenge anytime you play against top players. You want to pit yourself against the best players in the world
“It’s an exciting challenge when you play against the best players in the world and the best team in world like Spain.
“I think everyone is looking forward to the game and all the players are excited because it is a massive game to be involved in.”