Old fellow in ME sultanate (4)
I believe the answer is:
oman
'me sultanate' is the definition.
(Sultanate of Oman, Middle Eastern country)
'old fellow' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'fellow' becomes 'man' (fellow can mean a man).
'o'+'man'='OMAN'
'in' acts as a link.
(Other definitions for oman that I've seen before include "Former Gulf country, Muscat and --" , "Gulf sultanate" , "Arabian peninsula country" , "Nation" , "Muscat's country" .)