Moyes was the man chosen to fill the large void left by Sir Alex Ferguson, who won 38 trophies during his 26-year reign at Old Trafford.
"It is the end of a legend," said Holloway. "Ferguson has left a legacy behind him.
"But David is a fantastic manager and he has decided that is what he wanted to do. It was an honour for him to get the job and good luck to him, but not this weekend.
"Only time will tell for all of us what we leave, the mark we leave at each club that we work for.
"I hope Dave leaves a fantastic mark on Manchester United. He has worked so hard, he deserves it and good luck to him, but I am more concerned about my team."
United are just a point better off than Palace heading into Saturday's clash at Old Trafford, but Holloway isn't reading too much into that.
"At this moment in time they are in a transitional period," he said.
"They've got a new manager, who was chosen by the last one - you don't get much better on your resume than that. To hear 'I want him to replace me' must be an honour.
"But the fact of the matter is David has to make his mark on Manchester United - I've got to make my mark on Crystal Palace.
"Is it a good time to play them? I will tell you after the game."