I don't think Dortmund would do anything we asked them not to...football is big business and burning bridges unnecessarily is not a good business practice..I would imagine that City would want to keep this news quiet until our season ends. It could place unnecessary pressure on the other forwards and become a distraction.
But if it's being finalised soon (for instance due to a release clause deadline) then I do wonder how it's going to be leaked out.
I wouldn't put it past Dortmund to make a poorly timed statement just to screw us over.