Athletic are seeking a win to finish in the top eight of the Europa League after the group phase.
Valverde said: “The important thing is to finish in the top eight and the best thing is to win. Then, in terms of the crossings, it is already stipulated how you can have them. Now you don't know how your rivals can finish behind or there is no guarantee that it is better to be eighth than third."
On Williams, he continued: “For players who have a one-on-one like his, it’s important that they take on opponents and make the opponent think they’re going to get away from them at speed.
"There’s nothing defenders fear more than running backwards . A defender always wants to run forwards to limit the damage. Defending is much easier than attacking, and defending in a one-on-one, while difficult, is easier than getting past an opponent in a one-on-one. There are very few players who are capable of saving an opponent. They are chosen.
"It’s difficult to find people like Nico, who they put a player on and cover in case he gets out of there. He’s a guarantee for us.”
On Viktoria Plzen, Valverde added: "They are teams that play power to power and are very strong in tackles. You have to be very strong in tackles, in one-on-ones and divided situations. We saw that against Slavia Prague. When teams try to confront you from too high up and they play well, they can create problems for you."