One involved in open case (7)
I believe the answer is:
patient
'case' is the definition.
(a medical case)
'one involved in open' is the wordplay.
I cannot really see how this works, but
'one' could be 'i' (roman numeral) and 'i' is found within the answer.
The remaining letters 'patent' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for patient that I've seen before include "Calm" , "Cool" , "One receives medical care" , "Uncomplaining; invalid" , "Willing to wait" .)