The 20-year-old has attracted attention from Premier League clubs including Arsenal and Chelsea after impressing with the Bundesliga club this season.
Voller has said that he is unable to rule out interest for Bailey, who has found the net nine times so far this term.
"We would be doing bad work if other clubs were not interested in our players," the director told German source Bild.
"Leon Bailey is not the only one. But he loves this team and he needs his teammates. He gives it back and that makes him all the more valuable to us.
"We're happy with his development. We had to sign him in the winter last year because of the threat of losing him to a competitor."
Bailey's last strike for Leverkusen came in a 4-1 victory over Hoffenheim last weekend, the club's eighth win of the campaign.