Moody resigned as Palace's sporting director on Thursday amid allegations of sexism and homophobia against him and Malky Mackay during their joint tenure at Cardiff.
The Football Association has confirmed an investigation into a dossier of allegations submitted to the governing body by Cardiff bosses.
Mackay was all set to be appointed Tony Pulis' successor at Palace, but the club have now pulled the plug and are looking elsewhere.
Millen admitted Palace could now seek a direct replacement for Moody, as well as a new manager.
Admitting Moody's departure leaves a chasm, Millen said: "Iain was brought in to do a job to recruit and scout players, and Iain was experienced at that job.
"The chairman will now have to look at that situation, to see whether he wants to bring someone in."
Palace's managerial search is back to square one after the FA investigation ruled Mackay out of the running, with Chris Hughton now among the new contenders.
Millen admitted Mackay's managerial style would have suited the Selhurst Park club perfectly.
"Malky has got a good track record: I think he's used to working with players that want to work hard for him," said Millen, who will take charge of Saturday's home Premier League clash with West Ham.
"The way he set his teams up, they were successful and organised.
"And that's our DNA as a club and a squad, to make sure we work hard for each other, there's a great togetherness in the group.
"That really suits the type of players we've got here
Whoever comes in will need to work within those boundaries
"Each day something has unfolded, something has come out, so it's been difficult.
"I had a brief chat with the players about staying focused, and the lads have been fine, they are resilient as a group."
Source : PA
Source: PA