The problem will solve itself by the time the deadline comes and the bug is not fixed. Meanwhile, don't promise anything, don't commit to anything but don't bu

The problem will solve itself by the time the deadline comes and the bug is not fixed. Meanwhile, don't promise anything, don't commit to anything but don't burn any bridges. Be professional, explain what do you think it is, what might be wrong and why is it hard. "This bug will require a longer investigation and we cannot commit to any timeframe for its resolution" (unless you have a fallback/workaround ready or it is something you don't expect to be complicated)