The Belgian impressed in the Bundesliga last season during a season-long loan at Werder Bremen.
"We made no secret of our interest in Kevin De Bruyne right from last summer," Voller told Germany's Sky Sport. "There are many clubs interested in him.
"Regardless of our league position, we're always looking for new players.
"It's possible that we do sign somebody this winter, but then again, we could go into the second half of the season with the same team and look to do something next summer.
"If you do anything, then it's got to be a top alternative to what we've already got here."
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