In the four years the Brazilian has spent at Madrid, Kaka has failed to meet the expectations which stemmed from his 62million euro (£53.5million) transfer from AC Milan in 2009.
He started just 14 games in all competitions last season and further question marks about his future have been raised since the club signed attacking midfielder Isco.
Speaking during an interview with Gol Caracol de Colombia, Perez defended the signing of Kaka, pointing to the player's marketing appeal. He also highlighted the difficult circumstances he has had to cope with at Madrid, and said he hopes he will experience a resurgence in form next season, when he will get the chance to work again with Carlo Ancelotti, his former coach at Milan.
He said: "Kaka is a phenomenon, but he got injured in the last World Cup and had to have an operation on his knee.
"Then [Mesut] Ozil arrived and took his place in the team from him, but he is still one of the greats of the game. He is the second most followed footballer on Twitter, after Cristiano Ronaldo.
"He is charming and excites the fans. I'm optimistic that, under Ancelotti, who knows him very well, he can be the same magical Kaka again that we signed."
On Friday, Madrid completed the signing of 23-year-old Asier Illarramendi from Real Sociedad, the fourth player under the age of 24 that Madrid have bought this summer.
The president explained why Madrid have looked to youth.
"We have signed young players that are hungry to achieve and that's vital so that our established players don't get too comfortable. That mix of youth and experience will raise the team's quality," Perez said.
And he looked forward to the new season with Ancelotti in charge, adding: "We are beginning a new era after Mourinho's departure. We have another coach, who is also very demanding, and we are very excited."