Decline among lesser Germans on reflection (7)
I believe the answer is:
regress
'decline' is the definition.
(regressing is a kind of declining)
'among lesser germans on reflection' is the wordplay.
'among' indicates the answer is hidden within the clue.
'on reflection' says the letters should be written in reverse.
'sserger' can be found hidden inside 'lesser germans'.
'sserger' in reverse letter order is 'REGRESS'.
(Other definitions for regress that I've seen before include "Lose ground" , "Go backwards, disimprove" , "Get worse or fall back" , "Return to a former or less developed state" , "Revert, throw back" .)