One of these Championship clubs is potentially just 90 minutes away from a Wembley date with either Liverpool or Manchester City.
Palace currently hold the advantage in terms of scoreline, having won the opening leg between the two sides 1-0 at Selhurst Park.
However, Cardiff now have home advantage and have only lost on two occasions at the Cardiff City stadium this season.
Mackay's opposite number Dougie Freedman has made several changes to his starting lineup in recent weeks, although he is expected to name the strongest side possible for the trip to Wales.
Despite reported interest from Manchester United, Nathaniel Clyne is expected to start at right-back.
Cardiff: Heaton; McNaughton, Hudson, Turner, Taylor; Conway, Gunnarsson, McPhail, Whittingham; Earnshaw, Miller.
Palace: Lewis; Clyne, McCarthy, Gardner, Parr; Zaha, Garvan, Ambrose, Scannell, Murray, Martin.
Sports Mole says: 3-1