Legia lifted their 20th Polish Cup trophy on Tuesday with a 6-5 penalty shootout win over league leaders Rakow Czestochowa, after the game had finished goalless.
Players rushed onto the pitch after the final penalty kick was saved by Legia keeper Kacper Tobiasz (20). Mladenovic was approached by several Rakow players and the Serbian international responded by punching three of them, videos posted on social media showed.
Mladenovic, who was also fined 120,000 zlotys ($28,925), has been suspended from the league and cup, PZPN said, and will miss the opening games of the 2022-23 season, which starts in Poland in late July.
He issued an apology on Thursday.
"I apologise for my behaviour to the players, above all to Marcin Cebula (27), Wiktor Dlugosz (22) and Jean Carlos (26), and to the Rakow Czestochowa staff, including coach Marek Papszun," Mladenovic wrote on Instagram.
"I am aware that this was unacceptable. This is not how any sportsman should behave. I also apologise to the players of my team, my staff and the fans for representing the colours of Legia Warsaw in an unworthy manner."
Legia, 15-times Polish champions, are currently second in the table, 11 points adrift of Rakow with four games remaining in the season and little chance of regaining the title they last won in 2020-21.
