Bayern Munich have agreed a fee of £54.8m with Manchester City for Leroy Sane, with the German set to sign a five-year deal at the club.
The Bundesliga champions will pay an initial fee of £44.7m (49m Euros), with a series of performance and trophy-related add ons.
Sane has missed most of the current season with injury but was one of the key players as City won the Premier League and FA Cup last year.
Guardiola is disappointed that the Germany international will leave the club for Bayern.
He said: “‘I’m so disappointed. When we make an offer, it’s because we want him; he’s got a special quality that is difficult to find.
“We tried before the injury [and] the surgery and after that, and he rejected this offer.
“He has other wishes, and I understand [but] we want players who want to commit and achieve our targets.
“I love him so much, he’s incredible, I’ve nothing against him – he wants another adventure.
“That happens, and we’ll help him while he’s here, and focus on the players who want to stay.