The Azzurri goalkeeper left AC Milan at the end of the 2020/21 season and the Ligue 1 giants signed him as a free agent.
Despite Donnarumma joining a club that were runners-up in the 2019/20 Champions League, this transfer has not impressed the former Roma, Sampdoria, and Inter attacker.
“Why, if he is the best goalkeeper in the world, aren’t Bayern Munich, Real Madrid and Barcelona after him,” Cassano said on Twitch channel Bobo TV.
Donnarumma was voted Player of the Tournament at Euro 2020 as Italy went on to win their first European Championship since 1968.
The prodigious goalkeeper came through the AC Milan youth academy and played for the senior squad from 2015 until this year.