Head of recruitment Iain Moody, who worked for the Scot during his time at Watford before making the switch to Cardiff with him in 2011, has been replaced by 23-year-old Kazakhstani Alisher Apsalyamov.
Cardiff declined to comment on the matter when contacted by Press Association Sport.
The reasoning behind Moody's suspension is unknown but it is understood Apsalyamov, who is thought to be a friend of owner Vincent Tan's son and appears to have no previous experience in football, has taken over from him in an acting capacity.
Apsalyamov joined the club in February but his name does not appear on a list of key staff members on the club's official website.
Mackay has regularly praised Moody's scouting and recruitment work at the south Wales club, where he has helped to secure the likes of Steven Caulker, Gary Medel, Kevin Theophile-Catherine and Fraizer Campbell.
The loss of Moody has seen several bookmakers install highly-rated Mackay as the favourite to be the next Premier League manager to leave his post.
But while he is understood to be disappointed by events, he will be in charge when Cardiff face Chelsea a week on Saturday.
All this comes just a matter of days after it was revealed Tan and the Bluebirds squad had been at loggerheads over end-of-season bonus payments.
Mackay confirmed following Saturday's 2-1 defeat to Newcastle that a resolution has been reached over the issue, but Cardiff's players are reportedly no longer happy for Tan to be in the dressing room on matchdays.