Argentine striker Tade completed a move to Chloorkop on January 30, something Johnson said he expected to happen.
"When he arrived I spoke to him about the possibility of moving away from Durban, so we knew he won't stay with us too long, but we didn't have a time frame," Johnson said.
"The deal to Sundowns was concluded five hours before we faced Pitso's side, to show how hard it was for us."
When asked if he was involved in the decision to sell Tade, Johnson said the club made the decision like any other team in the world.
The coach also revealed that newly signed Zimbabwean attacker Talent Chawapiwa is part of the plan to prepare for life after Tade, but he's not a replacement.
"Chawapiwa is not a replacement, he's just joined other exciting players we have in the team, definitely he's not a replacement," Johnson added. "He's very talented though and on Saturday he could get his debut."
Johnson also spoke about former Orlando Pirates and Cape Town City defender Tshepo Gumede, who is currently training with the club and a free agent.
"We are still looking at him from his off-the-field lifestyle before we make any decision," he concluded.