Usuthu boss Lunga Sokhela has confirmed Sundowns have approached the Durban-based outfit regarding acquiring Tade.
Asked whether AmaZulu will sell Tade to Downs, Johnson said: "We don't know what the future holds."
Usuthu handed champions Downs their first league loss of the season last night with a 2-0 scoreline in Tshwane.
Johnson notably introduced Tade off the bench at Loftus Versfeld Stadium, and he insists the transfer speculation had nothing to do with his decision.
"There's been talks about Tade ever since he started playing for us," Johnson said of the Argentinian, who is also reportedly on Orlando Pirates' radar.
"Coming from the bench had nothing to do with what was said about him."
He added: "Tade is still trying to get his fitness back after suffering an injury. Sometimes you need to freshen up players."
Tade has scored seven goals so far in his first season in South Africa following his arrival from New Zealand's Auckland City in July 2018.