Spirit in bottle, German one, say, upended (5)
I believe the answer is:
genie
'spirit in bottle' is the definition.
'german one say upended' is the wordplay.
'german' becomes 'g' (abbreviation).
'one say' becomes 'eine' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'upended' says the letters should be written backwards (in a down clue, letters go up).
'eine' backwards is 'enie'.
'g'+'enie'='GENIE'
(Other definitions for genie that I've seen before include "Arabian goblin, may be in a bottle" , "Magical servant" , "Bottled spirit?" , "Spirit with the power to grant wishes" , "Magical Eastern spirit with strange powers" .)