Atletico Madrid coach Diego Simeone has said it made “no sense” for games to go ahead at the weekend, and Barcelona’s Hansi Flick said he would have cancelled them.
Real host AC Milan in the Champions League group stage on Tuesday.
Ancelotti won eight trophies, including two Champions League titles, as Milan manager from 2001 to 2009.
His Real team lost 4-0 to Barcelona on 26 October, and two days later Real striker Vinicius Jr finished second behind Rodri for the Ballon d’Or.
Football matters have since been firmly put in perspective by the tragedy in Valencia.
“It was supposed to be a special game for me, facing Milan. But there is no meaning in talking about football now,” said Ancelotti.
“It has been a difficult week, not because of what happened with the Ballon d’Or or El Clasico. It happened and that’s that – congratulations to the winners.
“Our sadness is not about that. It is for what is happening here in Spain.”
Uefa has announced there will be a moment of silence held at all Champions League, Europa League and Conference League matches this week in memory of the victims of the flooding.
A year’s worth of rain has fallen in parts of the Valencia region.
On Sunday the king and queen of Spain were pelted with mud and other objects by angry protesters during a visit to the town of Paiporta – one of the worst-affected in Valencia.
Objects were also thrown at Prime Minister Pedro Sanchez, who was quickly evacuated from the area.
Barcelona experienced flooding on Monday after torrential rain.
More than 60 flights at El Prat Airport were cancelled, delayed or diverted and rail services were suspended.