Maintain one putting money aside must suffer initial small loss (4)
I believe the answer is:
aver
'maintain' is the definition.
(averring is a kind of maintaining)
I don't understand how the rest of the clue works.
(Other definitions for aver that I've seen before include "State decisively" , "Declare or insist" , "State (to be the case)" , "'Affirm, assert (4)'" , "Formally state" .)