The chap dropped round at the beginning of the week (6)
I believe the answer is:
Here is my best explanation:
'the chap' is the definition.
('fellow' can be a synonym of 'chap')
'dropped round at the beginning of the week' is the wordplay.
'dropped' becomes 'fell' (I've seen this before).
'round' becomes 'o' (round can mean a round object**).
'at the beginning of' says to take the initial letters (I've seen 'at the beginning' mean this).
The first letter of 'week' is 'w'.
(Other definitions for fellow that I've seen before include "college type", "Chap", "Kind of associate, may be a traveller with communism", "Bloke; senior member of college", "Don", "Relating to a person in the same situation as oneself", "Comrade", "Informally, a man, or the other of a pair", "Companion or associate" and "The other of a pair - just a chap".)