According to reports, an appointment is expected sooner rather than later, leaving Harris - if it is to be the 42-year-old - with at least six weeks to assess his squad before the January transfer window.
But which of his old Millwall players might he want to join him at the Cardiff City Stadium?
HITC Sport takes a look, below...
George Saville (Middlesbrough)
Saville had three separate spells at Millwall - all but one of which occurred during Harris's reign. The central midfielder was sold to Middlesbrough last summer for a reported £8 million fee, but has only started six of the 15 Championship games for which he has been available this season. Cardiff's engine room is perhaps not their most well-stocked position and a Harris-managed Saville, who scored or made 13 goals in 64 games under the Essex native, could improve them in that area.
Jed Wallace (Millwall)
Arguably Millwall's best player this season, Wallace has scored or made eight goals in 14 league outings. The winger/attacking midfielder has had interest in the past and more could be on its way if his recent form continues. Cardiff may be among the suitors - especially if Harris takes charge - even if they are already blessed in Wallace's position.
Tom Bradshaw (Millwall)
Bradshaw's Millwall career has finally taken off, having scored seven goals in his last five games (although only one of those arrived during Harris's reign). Cardiff will hope that Warnock's exit can have a similar effect on Robert Glatzel and Gary Madine. But a striker could be high on the new manager's list should it not. Bradshaw was born in Shrewsbury but has three caps for Wales and may be attracted by a move to Cardiff, who will recall him scoring twice against them earlier this season.
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