Bielsa worked with Pepe at Lille.
Ahead of Monday's FA Cup tie, he said: "Pepe is a great player with big resources and is a goalscorer. A player who is able to unbalance a match.
"Obvious skills, when you have all of these skills in one player, the value is £70m. It was just a matter of time before he showed those skills. One thing is to have the skills, another thing is to have the skills and show them on the pitch. He does both. He has clearly shown his skills and is at a club where he deserves to be."