The Ajax midfielder has agreed a deal to join Barca for the 2019-20 season in an €86 million (£75m/$98m) deal, but De Jong confirmed in an interview he held talks with both Paris Saint-Germain and City manager Guardiola before choosing LaLiga's leaders.
Valverde was unimpressed with this revelation, telling reporters: "You cannot talk to a player who has a contract. It's not in my code. Everyone has their way of acting. I have nothing more to say."
Ahead of City's Premier League game away to Newcastle United on Tuesday, Guardiola was asked to respond to Valverde's comments.
"No answer," said the former Barca coach. "No answer to that, he's my friend, so no problem.
"De Jong will be a Barcelona player. It's finished. I don't want to talk about it; it's over. Not our player, not our business, [we] focus on Newcastle game.
"First of all, I'm not involved in negotiations. I give my opinion and we do our best and I'm so satisfied. The club worked incredible and sometimes they come, sometimes they don't, it's not a problem at all.
"All the big clubs sometimes decide with players and the reality is what it is, sometimes it's not possible. We have enough players to play [on Tuesday]."
Guardiola added that club captain Vincent Kompany will not be fit for the Newcastle game, but said full-back Benjamin Mendy is "much better" following a knee problem.