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."