Italy coach Roberto Mancini was unhappy with supporters who jeered Leonardo Bonucci during the nation's 0-0 draw with Portugal in Milan on Saturday.
Bonucci, 31, spent last season at AC Milan after a move from Juventus, only to secure a return to Turin in August.
The move back to Juve has left a sour taste for some Milan supporters, who targeted the veteran defender with jeers during the Nations League clash.
Mancini criticised the fans and said there should never be a repeat when players are representing their country at the international level.
"It was a mistake for fans to be booing Bonucci," he told a news conference following the scoreless draw.