The 24-year-old appears likely to move to Bayern Munich, however when that move will take place remains unclear.
“Leroy says he doesn’t want to extend his contract. That means he’s going to leave,” Guardiola said.
“If we find an agreement with a club he will leave this summer, if not he’ll stay another year and will leave at the end of his contract.”
A suitable fee for the German winger is uncertain, but Bayern may be reluctant to spend big after the financial hit all clubs have taken as a result of the coronavirus pandemic.
Sane spent Thursday's (AEST) 3-0 win over Arsenal on the bench as an unused substitute as the Premier League restarted after its enforced COVID-19 hiatus, and his reluctance to stay at the club could significantly reduce his playing time.
He has yet to play since coming back from an anterior cruciate ligament lay-off, and Guardiola added that despite offers before an after his injury, Sane made it clear he wanted a new challenge.
"We want players who want to play at this club," Guardiola said.
"I have nothing against him, but he decided he wants another adventure for his career. We are going to count on the players who want to stay here.