I don't know if this is still the case, but I have flown on Lufthansa with a bicycle not in a box. That is also at odds with what I see on their web site right now (https://www.lufthansa.com/br/en/sportgepaeck): "bicycles will only be accepted if they are packaged in a suitable bicycle case or a similar container. Lufthansa is not able to provide you with packaging."