The Premier League club have already made contact with the German outfit to sign 22-year-old Germany international forward this summer.
"Andre Schurrle has probably signed a pre-contract deal with Chelsea," Kicker quotes Holzhauser as saying.
"It all depends on whether we let him go. We have received a concrete offer for a fee which we are considering.
"But the price alone is not decisive. We must also have alternatives, which we don't have yet."
Schurrle joined Leverkusen from Mainz in 2011.