The 18-year-old left Milan in a state of shock after deciding not to extend his contract with the club.
And he was barracked by Italian fans during Sunday's U21 Euros win against Denmark.
Pogba, however, says the goalkeeper deserves respect for what he has done in his short career and has tipped him to become the best in the world. The pair share the same agent, Mino Raiola.
Pogba posted to social media: "Donnarumma soon best in the [world]. Deserves only respect for all he's done until now."