One involved in obvious case (7)
I believe the answer is:
patient
'case' is the definition.
(a medical case)
'one involved in obvious' is the wordplay.
'one' becomes 'i' (Roman numeral).
'involved in' means one lot of letters goes inside another.
'obvious' becomes 'patent' (similar in meaning).
'i' put into 'patent' is 'PATIENT'.
(Other definitions for patient that I've seen before include "One getting medical care" , "Calm" , "one of interest to medics?" , "Enduring trying circumstances with an even temper" , "one receiving medical treatment" .)