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The 43-year-old was caught on camera committing the offence when shouting instructions to team-mate Manolo Portanova.
The Italian Football Federation (FIGC) opened disciplinary proceedings against Buffon earlier this year and he was fined €5,000 by the governing body last month.
It was announced on Wednesday that the veteran shot-stopper will also serve a one-game ban - against local rival Torino in Serie A on Sunday - after the Federal Court of Appeal upheld the appeal of the Federal Prosecutor.
Buffon has served as back-up to Wojciech Szczesny since returning to Turin from Paris Saint-Germain in 2019 and has made 10 appearances in all competitions this season.