Religious doctor claims one should get injected (7)
I believe the answer is:
islamic
'religious' is the definition.
(Islam is a religion)
'doctor claims one should get injected' is the wordplay.
'doctor' is an anagram indicator.
'one' becomes 'i' (Roman numeral).
'should get injected' indicates putting letters inside.
'claims' with letters rearranged gives 'islamc'.
'islamc' going around 'i' is 'ISLAMIC'.
(Other definitions for islamic that I've seen before include "Relating to Muslim religion" , "Of Mohammed's religion" , "Relating to Muhammad's religion" , "Relating to a particular religion" , "Concerning the Muslim religion" .)