Having clinched the signing of Conor Gallagher in August, Atletico are now chasing his former Blues teammate Fernandez.
Atletico plan to make an offer in January of a six-month loan with a permanent option included.
And Okdiario says Chelsea are receptive to the approach - as is the Argentina international.
With the midfielder no first-choice for manager Enzo Maresca, Chelsea are prepared to listen to offers for the midfielder.