The Bluebirds boss had claimed at the weekend he hoped to bring three new players to the club to fortify his team for the second half of their maiden Barclays Premier League season.
Cardiff beat West Brom 1-0 on Saturday to strengthen their bid for survival in the top flight, but transfer spending has been in the spotlight at the club before this season, and owner Vincent Tan's eagerness to rein in spending has surfaced once again.
Head of recruitment Iain Moody was replaced by Kazakh 23-year-old Alisher Apsalyamov in October, and Mackay will have little option but to sell if Tan refuses to be swayed on his insistence there will be no budget for the Scot to utilise.
Chief executive Simon Lim released a statement outlining the stance on spending in which he claimed Tan was jolted by Mackay's announcement that he would seek backing from the board for squad strengthening.
Lim said it was Tan's view that the club overspent in the transfer market by £15million ahead of the season.
"Tan Sri Vincent Tan was extremely upset to read quotes from the manager concerning the possibility of new recruits, before he had been informed whether funds would be made available," Lim said.
"He believes that doing so unfairly raises supporter expectations, placing unnecessary pressure on the club.
"His view is that due to the funds already committed, including the originally authorised summer transfer budget of £35m that rose to £50m in total, including add-ons, the manager has been fully supported.
"The overspending of £15m has upset Tan Sri greatly, resulting in the removal on Iain Moody as head of recruitment. As such, he has stated that not a single penny will be made available in January.
"Having been the highest-spending promoted club and the seventh-highest spender in the Premier League last summer, the owner believes that the manager has been given the best possible chance of retaining our Premier League status."
Cardiff brought players including Steven Caulker, Gary Medel, Kevin Theophile-Catherine and Andreas Cornelius to the club during the summer.
Mackay's team stand four points outside the relegation zone, and Mackay was hoping he would receive the board's cheque-book backing midway through the campaign.
The fact Malaysian businessman Tan, through Lim, has indicated that will not be happening may be of some concern to the Scot, in his third season at the club.
Speaking at the weekend, Mackay said: "It would be great if we can bring in three quality additions to the squad.
"I would look to strengthen all three departments in terms of a defender, a midfielder and an attacking player.
"I will talk to my chairman (about January) who will then discuss it with his board of directors and our owner and I will take my lead from them.
"It's up to them then what financially they want to spend in January. I've got my lists of players, whether they be permanent targets or loans for various positions. We've got to try and strengthen again.
"We are a first-time club so to speak. Everyone barring two other clubs has got a massive head start on us in terms of quality.
"They might only need to bring in one or two over a season. We had to bring in a group of eight players which was going to give us the chance to survive.
"You have a choice, do you invest knowing you have a really good chance of staying up or do you invest knowing you might go down and then have to build again?"
Looking at the January market, Mackay added: "People are leaving clubs for different reasons and overall you have to be careful. It's about bringing in another layer of quality to add to what we've got. I need to bring in guys who are going to add to that."
Mackay joined Cardiff in June 2011, and after missing out on promotion in his first season at the club, when his team suffered a play-off semi-final defeat to West Ham, he led the Welsh side to the 2012/13 Championship title.