The 43-year-old lifted the Champions League twice at the helm of the Blaugrana and could become the first coach in the modern era to claim the trophy for a third time this season, with his Bayern side set to face Real Madrid in the semifinals.
De Boer, who played alongside Guardiola at Camp Nou between 1998 and 2000, says the former Spain international's intelligence as a player has helped him to become a "genius" in the dugout.
"As a manager, Guardiola is a genius," the former Netherlands international told Sport1. "As a player he was always very intelligent on the pitch. Physically he couldn't match the more robust players so he had to be clever. He always thought three to four steps ahead and is still doing this as a coach."
Guardiola takes his Bayern side to Santiago Bernabeu to face Real Madrid in the semifinal first leg on Wednesday.