The Argentine forward is signing for Atletico Madrid for a fee that is an initial £64 million rising to £81.5 million.
Guardiola had previously stated that he hoped to count on Alvarez for this season, but could not convince the forward to remain as second fiddle to Erling Haaland.
"I don't know yet. We talk every day and see what happens. It (signing a replacement) could happen but it could not happen," Guardiola told reporters this week.
"I want to say the gratitude of Julian being two years here, we won everything together and his contribution has been massive.
“He's incredibly loved by the team for his behavior but like I said many times of many players he wants to leave and a new challenge.
"Atletico is a top club in Spain and Europe and when they suggested to me that he wanted to leave, imagine he stays here if he wants to leave? Both clubs are happy with the agreement, I look forward to see him back to say bye to all of us. It was a joy to work with him. I learnt a lot from him and hopefully he can find what he was looking for."