With just two weeks before the transfer window closes, Millen believes that it is important for the new manager to bring in the players that he wants to fit his system.
"This is the problem with changing managers," the Daily Mail quotes Millen as saying. "You bring in players to suit the system you play and if you are bringing in a different manager with different philosophies, then maybe they won't suit that.
"With the window shutting at the end of this month, the appointment is important so they have a little bit of time to bring in new players."
The Eagles came close to sealing a draw against Arsenal at the Emirates on Saturday under Millen's leadership, but Aaron Ramsey found a late goal to secure a 2-1 victory for the Gunners.