Clay beneath motorway in African country (4)
I believe the answer is:
mali
'african country' is the definition.
(country in Africa)
'clay beneath motorway' is the wordplay.
'clay' becomes 'ali' (Muhammad Ali was born Cassius Clay).
'beneath' says to put letters next to each other (in a down clue).
'motorway' becomes 'M' (as in motorway names - M1, M4 etc).
'ali' put after 'm' is 'MALI'.
'in' is the link.
(Other definitions for mali that I've seen before include "African state's" , "A state" , "West African country, capital Bamako" , "Land" , "African country, former French colony" .)