The Bluebirds remain in pole position at the top of the table despite a recent blip in form which has seen them only take four points from the last available 16.
However, Mackay is resisting calls to rest Whittingham, who he believes is one of the best players in the division, even though he has played in all but one of Cardiff's 35 league games.
"Peter is among the best players in his position in Championship football," Mackay told walesonline.
"He is and will continue to be one of the first names on my team sheet.
"Other Championship teams would like it if they saw he was not in our starting line-up.
"That would give the opposition a lift and that's not something we wish to do."
Cardiff drew their match against Derby 1-1 last Tuesday and did not play at the weekend, but are still five points ahead of second-placed Watford after their 2-1 defeat by Blackpool.
Cardiff will, however, be boosted by the return of striker Craig Bellamy and captain Mark Hudson who have recovered from knee and ankle trouble respectively.
"Craig had a few days away for rest and recuperation but he'll be okay for Leicester," Mackay said.
"He is a player who works to keep his body in amazing condition and he will be involved on Tuesday.
"Mark Hudson, too, has made good progress after injury and will be back in full training and in the squad for the Leicester game."