Barca have been strongly linked with a move for their former academy player, with reports in Spain claiming the teenager wants to return to Camp Nou.
City are determined not to let one of their brightest prospects go and have been locked in talks with Garcia, whose current contract ends next summer.
Guardiola insists City are working hard to tie the centre back down to a new long-term deal.
“We have one more year - if they want him they must call Txiki (Begiristain, sporting director),” he said.
“We’ll try to convince him to stay here for many years. I’m confident he will stay, but it’s his decision.”
City have already seen one of their stars leave after Leroy Sane refused to commit his future to the Etihad. The German completed a £45million move to Bayern Munich last week after being valued at £140million last summer.
Garcia has forced himself ahead of John Stones in City’s pecking order this season, with Guardiola believing he will develop into a top-class defender and the club will be reluctant to let 19-year-old Garcia run his contract down.
Guardiola added: “He knows we want him, but it was the same with Leroy (Sane). He didn’t want to stay.
“He knows, his agent knows and his family knows we want him. He’s young.”