The attacking midfielder has been linked with a number of big clubs and the Bundesliga side would not stand in his way if one of Europe's finest made a move for him
The Germany international, 19, recently admitted that it would be hard to reject one of Europe's superpowers if there were to make a move for him and the S04 chief confirmed that they are ready to open talks if a good offer comes in.
"It is not necessarily a bad thing when a club like Chelsea are interested. Julian is an important player for Schalke and we obviously want to hold on to him," Tonnies told Express.
"However, if you want the best for someone, you will have to consider allowing him to move abroad at some point.
"What are we supposed to tell Julian when a club like Real Madrid make an enquiry for him? Tell him not to speak to them? That would simply be ridiculous. Those days are behind us now."
Draxler signed a new deal with Schalke until June 2018 earlier this summer.