Tan removed Mackay from his post in December 2013, accusing him and recruitment chief Iain Moody of overspending by £15 million.
Those accusations have always been denied by the pair,but they both issued unreserved apologies to the club's Malaysian chief last week, with Mackay opting to drop legal proceedings against Cardiff.
And, despite Cardiff claiming just 12 points under replacement Ole Gunnar Solskjaer, Tan has laid the blame for the club's return to the Championship at the feet of Mackay.
"The main person responsible for relegation is Malky Mackay, the hero of fans," Tan told Wales Online.
"They should ask why he apologises? They should find out from him.
"Legally, I'm not supposed to say. I wish I could say, but I can't. Ask him why he apologises.
"His friends supported him to be a big hero, unfortunately their hero almost killed this club and I was not going to be putting more and more money in."
