Gueye says the Toffees winger is capable of becoming one of the world's best players.
He stated: "I challenge (Ndiaye) every game, every time we play. I'm always speaking to him. He's a good boy, he listens a lot and, yeah, I'm like his... grandbrother. I always knew he would be successful here at Everton and, honestly, I don't think he's shown his best yet.
"I train with him every day so I see his quality every day and I can see what he is capable of. He just needs to believe in himself, keep working hard and have high expectations of himself. I told him when he first arrived here that he can be the next African Ballon d'Or winner, because he has the quality, he has the technique, he has the skills and everything. He has a combination I've never seen before.”
Gueye also told the club's website: "He's a humble guy. A very, very good guy. He's not shy – he likes to play and joke with everyone. Nobody ever has a problem with him because he is humble and always keeps working hard. You see in those videos even from when he was very young how hard he works and it's because he always wants to be better."