Amid interest from Manchester City and Liverpool, there have been claims negotiations over Musiala's new have stalled.
The Germany attacker's current contract expires in 2026.
Eberl told ZDN: "From the outside, you think things are stalling, but inside we are continuing to work calmly. And at some point there will be a surprise."
When asked about a possible future exit clause for Musiala, Eberl replied: "I will not comment on any of the contract contents. We have learned how to properly deal with this speculation from outside. Internally, we stand together strongly."
In general, the 51-year-old was optimistic: "We are having great discussions - completely transparent and completely open. I can't say which way the decisions will go, but the discussions are on a really good basis. And that's what matters."