Juve fans barracked Sandro during the Coppa Italia semifinal win against Lazio on Tuesday.
Allegri said: "I'm sorry for the boos for Alex Sandro, he won five Scudetti with Juventus and deserves respect.
Advertisement
Advertisement
"Tonight, among other things, he came in very well.
"I have respect for the fans and the fans must encourage the team. Many things can be said, but in terms of commitment we have never failed. The boys played tonight as a team, with great humility and determination.
"They should enjoy it because they fully deserved it."