La Roja will enter the tournament in Brazil as the European and world champions, having lifted the World Cup in 2008 and European Championship title in 2012.
"If Spain win the World Cup it will be an amazing moment," he told reporters.
"They will be for sure the best national team of history. We had the opportunity to go for the second one with France and we know how difficult it is to handle the pressure."
Desailly won the World Cup with his country in 1998.