The club have released the pair from their playing contracts due to personal reasons.
Both Sinclair and Dowdridge, who had been living in Hawks accommodation in Winchester, were keen to move back to their respective family homes in London amid the coronavirus pandemic.
The National League South season is currently suspended for two weeks but the duo will not be returning to the club should the campaign restart.
The pair arrived at Westleigh Park in the summer after impressing on trial although were unable to nail down regular starting spots.
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Forward Sinclair was forced to settle for a bit-part role, mainly featuring from the bench, while Dowdridge was sent on loan to Isthmian League Premier Division Bognor following his arrival.
The pair follow defender Moussa Diarra in leaving the club after he completed a move to former club Woking.