It's Wednesday afternoon and so far we've got no hard news on the Eagles next defensive coordinator. The speculation has been that the team was waiting for the Super Bowl to end because they planned to target one of the assistants on the 49ers or Ravens.
One of the speculated candidates was 49ers secondary coach Ed Donatell. There's been no indication as to whether the Eagles have reached out to speak with him, but the Saints have... and the 49ers said no.
Under NFL rules, secondary coach to coordinator is not a promotion and therefore teams can block their guys from interviewing.
Per NFL rules, there are head coaches and assistants. Teams can't block assistants from interviewing for head coaching jobs, but they can block them for interviewing for other assistant jobs, even if those jobs would in reality be a promotion.
So if the Niners say the Saints can't talk to Donatell, it's fair to speculate that they would do the same if the Eagles wanted to hire him.