Morally weak following deceptive person turning up (5)
I believe the answer is:
frail
'morally weak' is the definition.
(I've seen this in another clue)
'following deceptive person turning up' is the wordplay.
'following' becomes 'f.' (used when citing page numbers etc).
'deceptive person' becomes 'liar' (I've seen this in another clue).
'turning up' shows that the letters should be reversed in order.
'liar' in reverse letter order is 'rail'.
'f'+'rail'='FRAIL'
(Other definitions for frail that I've seen before include "rush" , "isn't sturdy" , "Feeble - basket" , "Slight" , "Physically feeble" .)