Ivan Leko was impressed by Seys's performance in the World Cup quarterfinal against Spain, where he played 30 minutes. Leko believes Seys's abilities were evident even in a limited role. "He played 30 minutes in the World Cup quarterfinal against Spain, but what a half hour it was!" Leko exclaimed.
Seys also faced off against Lamine Yamal in an oefenwedstrijd against Feyenoord. Leko praised Seys's display, saying that he did fantastically well. "We watched that match the day after our friendly against Feyenoord. The atmosphere was fantastic, because Joa did fantastically against Lamine Yamal, one of the best players in the world."
Leko is confident that Seys has the talent, character, and mentality to succeed at the highest level. He believes that Seys has the potential to reach the absolute top of the Premier League. "I see Seys reaching the absolute top of the Premier League: I think he has no ceiling. He has the talent, the character, and above all: the right mentality. He comes here often as the first one and leaves as the last one," Leko said.