The Swede left the Nou Camp under acrimonious circumstances to join AC Milan after a falling out with the Spaniard in August last year, and both parties have since had frosty relations.
However, Ibrahimovic has had a change of heart, praising the 40-year-old tactician for his record with Barcelona.
"Barca are the best team in the world," the star striker said to La Gazzetta dello Sport.
"I already knew [that] when I got there, and when I left. What happened, happened. Guardiola is a fantastic trainer, the problems between us were different."
Ibrahimovic admitted that he was pleased at drawing Barcelona in Group H of the UEFA Champions League, and was confident that AC Milan would still progress further in the competition, crowing: "Think of today. Guardiola is doing well at Barcelona, and me too. We must move forward and not look back.
"Milan are strong and we are still growing. We [have] made good signings and I hope they can adapt well in the group."
The two European big-wigs will face off on 13 Sept at the Nou Camp.