Mbappe was widely tipped for a move to the Spanish capital but signed a contract extension until 2025 at PSG last week in a dramatic U-turn, a decision that irked many Real players and fans.
"Real Madrid will always continue to work on having the best players, but today Mbappe is already forgotten," Perez told reporters after a Vinicius Jr tap-in gave them a 1-0 win.
"Nothing has happened, Real Madrid have had a perfect season and that is a forgotten issue, there is only a Real Madrid party."
Mbappe's choice to stay at the French champions has triggered a war of words between the parties involved after LaLiga president Javier Tebas said they would file a complaint against PSG to UEFA because the deal "attacked the economic stability" of the European game.
Ligue 1 president Vincent Labrune hit back at Tebas on Thursday, saying his denigration of the French league and its players was "unacceptable".