Clinic's fourth ruse involved health worker (5)
I believe the answer is:
nurse
'health worker' is the definition.
'nurse' can be an answer for 'worker' (I have seen 'Medical worker ' mean 'nurse' so perhaps 'worker' could also mean 'nurse'). I'm not sure about the 'health' bit.
'clinic's fourth ruse involved' is the wordplay.
'clinic's fourth' becomes 'n' (4th letter of 'clinic').
'involved' indicates anagramming the letters (involved can mean confusing or complex).
'ruse' is an anagram of 'urse'.
'n'+'urse'='NURSE'
Can you help me to learn more?
(Other definitions for nurse that I've seen before include "Professional carer" , "Trained carer" , "One tending the sick" , "care worker" , "Entangle" .)