Real Madrid striker Karim Benzema has urged Kylian Mbappe to stay with Monaco.
The teen has been linked with Real and Manchester United.
But Benzema told RMC: "I've been told he is a phenomenon, a very good player," Benzema told RMC. "Honestly, I still haven't seen him. He's a young player. Football is really hard, especially at big clubs. I arrived at Madrid at 21. I had already done a lot of things at Lyon, but when I got here I got a slap in the face.
"My first year was too difficult. You're far from your family, it's not the same. Those who are next to you are there to take your place. It's very difficult. But from what people have said, he's a very good player, and I hope he'll have a great career, little by little.
"I think you mustn't leave too soon. Things go well, but the day when it goes less well, that's the problem. He's 18, how do you handle it when it doesn't go as well, when people don't speak as well about you, when you're put under pressure?"