Paris Saint-Germain coach Thomas Tuchel believes Kylian Mbappe will become the best player in the world, but said the attacker still needed to improve.
Mbappe, 19, has made an impressive start to the season with 13 goals in 11 games for PSG.
But the teenager was questioned by Spain and Barcelona great Xavi, who said Mbappe still lacked "football maturity".
In response on Monday, Tuchel backed Xavi, but said it was normal that Mbappe still had room for improvement.
"He's amazing. He's one of the best players in the world and he's going to be the best.
"Xavi is right. He needs to improve on everything, it's totally normal when you're 19."
Mbappe and PSG are set to take on Napoli in a vital Champions League clash on Tuesday as the French champions sit one point behind the Italian club in third place in their group.