Mackay's position looks increasingly precarious after the Scot was given an ultimatum by Tan to resign, or face being sacked.
Mackay, 41, then failed to turn up for his Friday morning press conference ahead of Saturday's trip to Liverpool, with his assistant David Kerslake attending but declining to answer any questions about the future of his boss.
Tan has made himself unpopular with Cardiff fans by changing the colour of the club's home kit from its traditional blue to red, as well as hinting he would be prepared to change the club's name in the future.
His decision to dismiss Mackay's head of recruitment Iain Moody in October and replace him with Alisher Apsalyamov caused further consternation, and should Mackay follow his old friend out the door, Supporters' Trust spokesman Phillip Nifield expects fans to make their displeasure known.
He told Press Association Sport: "If Malky Mackay is sacked I would imagine it is inevitable that the fans will make their voices heard.
"I would be astonished if that is not the case.
"I am sure there will be a few banners and chants in support of Malky and against the owner at Anfield, and I am sure there will be more of the same for the home game against Southampton on Boxing Day and it may not be pretty.
"It is tough enough trying to survive in the Premier League and there are concerns those efforts are being undermined by the owner."
By contrast with the owner, Mackay is a very popular figure among the Bluebirds' faithful having guided them back to the top flight for the first time since 1962.
And Nifield believes his popularity puts him on a par with Jimmy Scoular, who managed the club between 1964 and 1973, memorably helping the club beat the might of Real Madrid in the first leg of their 1971 Cup Winners' Cup quarter-final.
"I've been following the club for over 50 years and the only person who was maybe more popular than Malky was Jimmy Scoular, who managed the club during the 1960s and early 1970s.
"Obviously the game is very different now in terms of finances but Malky Mackay has built a real rapport with the fans, he has been a very nice man to speak with when the Supporters' Trust have had the opportunity to meet him. He seems to have a real empathy for the fans and they respond to that."
Nifield also revealed the Supporters' Trust are due to meet Tan at next weekend's home game against Sunderland.
He said: "The situation with Malky, whether he has been sacked or not, is an issue we will look to press. But also with the rebranding and the changing of colours from blue to red.
"He needs to redress what has happened and we would like him to change the kit back to blue from the start of next season, and have the team play in blue away from home this season.
"We also like the situation at our neighbours Swansea, where the Supporters' Trust have a stake in the club and a presence on the board. It is something we are envious of and would like to have at Cardiff."