It was easy to miss Gueye’s signing for P.S.G. this summer. The deal, for a not insignificant $35 million, to take him to Paris from his former club, Everton, went through on July 30. Everton was busy that day, announcing a coup of its own: the capture of the Juventus striker Moise Kean.

P.S.G., as it was all summer, was trying to keep track of the endless, spirit-sapping saga over Neymar’s future, waiting impatiently for Barcelona to make plain its intentions toward the striker. The signing of a defensive midfielder — especially a 29-year-old one — who had spent the last few years toiling in the mud and sawdust of the Premier League’s mid-table battleground could not compete for intrigue or attention. Gueye did not have a grand unveiling. Lines of fans did not materialize outside the Parc des Princes to buy a jersey emblazoned with his name. One day, he was at Everton, and the next day, he was in Paris. From the outside, it just kind of happened.

Internally, though, it was different. Tuchel had pulled out all of the stops to sign Gueye. P.S.G. had been scouting him for months. Tuchel had tried to bring him to Paris last January, but was stymied by Everton.

In the summer, he called Gueye, outlining his vision of what his role would be in Tuchel’s team, a personal touch that meant a lot to the player. Among his friends, Gueye is now teased for being something of a teacher’s pet. The hug will have given them considerable ammunition. On his first day, Tuchel told him “not to change” in his new environment. He wanted the rest of his team to adapt to Gueye, to be more like him, not the other way around.