Death of Diana would be the reason.
Just checked the team that day.
Niemi, Wright, Bollan, McCall, Petric, Gattuso, Vidmar, B Ferguson, Johansson, Durrant, Albertz.
The only Celtic players that made their 1st team were McBride & Burchill.
They also had two players sent-off (don't remember either) so not exactly one of our better days.