Voller insisted the transfer of Schurrle to Chelsea will only be sanctioned if the deal suits Bayer Leverkusen, after reports in recent days suggested an agreement was close.
Leverkusen officials, including Voller, were in London last week for talks with Chelsea. The Blues are willing to let De Bruyne leave on a season-long loan but the German club are thought to want the Belgian international on a permanent basis.
Speaking to TV show Sky90, Voller said: "The transfer of Schurrle is a question of the total package. There are some more items and De Bruyne is one of them.
"[De Bruyne] is a top alternative and can play a similar position like Andre [Schurrle]. If a good player leaves we've got to sign another good, or even better, player."
Schurrle has been a long-term target for Chelsea, and the west London club were thought to have had a bid rejected last summer for the 22-year-old.
Reports in Germany have claimed that he's already agreed personal terms with Chelsea, and many expect him to sign a five-year deal with the Stamford Bridge club.
But any agreement appears to hinge on De Bruyne, who is currently on loan in the Bundesliga with Werder Bremen.