Arrigo Sacchi is not surprised Gianluigi Donnarumma was jeered on his return to San Siro after suggesting the Italy goalkeeper "betrayed" Milan by joining Paris Saint-Germain.
Donnarumma arrived at the Ligue 1 giants on a free transfer in July after reaching the end of his Milan contract and failing to agree fresh terms with his boyhood club.
The 22-year-old made 251 appearances for Milan between emerging through their youth ranks in 2015 at the age of 16 and departing for PSG three months ago.
Donnarumma's reluctance to sign a new deal at San Siro, thus meaning Milan received no transfer fee, angered some supporters of his former club.
A section of Milan fans inside San Siro made that frustration known when whistling the young keeper every time he touched the ball for Italy in last week's Nations League semi-final loss to Spain.
Azzurri head coach Roberto Mancini criticised the supporters who booed their former hero, but Milan great Sacchi can understand the reaction.
"I have never jeered anyone in my life, but at times people do go looking for these insults," he said at the Festival dello Sport event in Trento.
"Evidently, there was a betrayal. In football and in everyday life, betrayal has to be repaid in kind. So let's not be shocked by a few jeers."
Despite his young age, Donnarumma has already appeared 218 times in Serie A and Ligue 1 combined since making his Milan debut in October 2015.
Only Samir Handanovic (219) and Inaki Williams (220) have featured more regularly in Europe's top five leagues across that period.
Donnarumma has kept 72 clean sheets in those 218 league games and has a save percentage of 72.72.
Eleven others to have played at least 100 times in that timeframe rank higher in that metric than Donnarumma, with Atletico Madrid's Jan Oblak (78.87) leading the way.
He earned his 38th cap for Italy in Sunday's 2-1 win over Belgium as the Azzurri finished third in the Nations League.
