Poor Jack is in depressed condition (7)
I believe the answer is:
lockjaw
'condition' is the definition.
(lockjaw is a kind of condition)
'poor jack is in depressed' is the wordplay.
'poor' is an anagram indicator.
'is in' indicates putting letters inside.
'depressed' becomes 'low' ('low' can be a synonym of 'depressed').
'jack' anagrammed gives 'ckja'.
'ckja' placed within 'low' is 'LOCKJAW'.
(Other definitions for lockjaw that I've seen before include "Serious condition" , "disease resulting" , "Form of tetanus in which mouth is tightly closed" , "Popular name for tetanus" , "Graphic word for tetanus" .)