Popular company's not in good shape (6)
I believe the answer is:
infirm
'not in good shape' is the definition.
'popular company's' is the wordplay.
'popular' becomes 'in'.
'company' becomes 'firm' (I've seen this before).
'in'+'firm'='INFIRM'
(Other definitions for infirm that I've seen before include "unstable" , "Doddery" , "Not well" , "Physically weak as from old age" , "Feeble, decrepit" .)