Formerly single, going round clubs (4)
I believe the answer is:
once
'formerly' is the definition.
('once' can be a synonym of 'formerly')
'single going round clubs' is the wordplay.
'single' becomes 'one' (I've seen this before).
'going round' means one lot of letters goes inside another.
'clubs' becomes 'c' (abbreviation used in card games such as bridge).
'one' placed around 'c' is 'ONCE'.
(Other definitions for once that I've seen before include "Cone (anag.)" , "not repeatedly" , "Long ago" , "In the old days" , "Sometime" .)