German media outlet Bild has learned that Mainz want €15 million for midfielder Johannes Geis.
The talented footballer has emerged as a top target for Borussia Dortmund and the Millionaires have now been informed of the asking price.
Mainz are not under pressure to sell their prized asset and will only let him leave if their valuation is matched.
Dortmund have already secured the signature of Bayer Leverkusen midfielder Gonzalo Castro and it remains to be seen whether they will splash the cash on Geis as well.
The 21-year-old has been in fine form this season, having managed 4 goals and 3 assists in 34 Bundesliga outings and he is now set to represent Germany at the Under-21 European Championship.
Germany have been made 9/4 favourites to lift the trophy at the tournament finals, but they will first have to negotiate a group that also contains Serbia, Denmark and Czech Republic.