Tierney came up against Mbappe in the Champions League with Celtic.
He told Arsenal's YouTube channel: "The one who posed the most difficulties? Kylian Mbappé. He was so fast, like his entire team. It's the toughest game I've played in my career, there was Daniel Alves and Mbappé on my side.
"If I learned from this meeting? Yes, great, we suffered 7-1. But when you face the best players in the world, you learn anyway whatever the outcome. But yes, it was hard, my most difficult evening."