PARIS — A few days before Paris St.-Germain traveled to Liverpool in September to begin its latest quest to win the Champions League, Dani Alves and Kylian Mbappé stood on a stage in a starkly lit room in the basement of the Parc des Princes.

In front of them, a crowd of dozens of journalists, social-media influencers and fashion bloggers milled around, watching freestyle soccer players run through their dazzling array of tricks. The décor was industrial chic. Exposed pipes ran along the ceiling. Goal posts and basketball hoops had been arranged to create a replica of an urban ball court.

Alves and Mbappé — alongside Wang Shuang and Marie-Antoinette Katoto, members of P.S.G.’s women’s team — were not there to play, though. They were there to stand, to pose, to model. For once, inside their home stadium, they were not the star attractions. All anyone cared about, really, was what they were wearing.