With Bayer now out of the Europa League, Havertz is expected to see negotiations over a move to Chelsea to accelerate.
However, Voller told Kicker this morning: "We have not made any decision yet. There is nothing new to say about it.
"I would like to repeat myself and say that he is a fantastic football player and we have a clear agreement with him and his representatives that he can only leave us if certain requirements are met.
"Otherwise he's staying here."
Havertz has a deal with Bayer to 2022.