Shonga finds himself currently without a club after being deemed surplus to requirement at Cape Town City.
The Zambian striker has been training with Usuthu with a view to signing a deal ahead of this upcoming season.
Shonga was tipped to be among the slew of new players unveiled by AmaZulu on Thursday but failed to agree to financial terms with the club, according to a well-placed source.
"The problem now is the issue of the salary. The parties are not on the same page in terms of salary package for the Zambian player", the source said.
"The negotiations are still ongoing."
Efforts to reach Shonga's agent, Karabo Mathang proved unsuccessful while Usuthu co-director Manzini Zungu sounded cagey when queried on a potential deal.
"We will invite the media if we do business in the transfer market. Thanks."