Marcelo reaggrevated a right calf muscle injury in Sunday's match at Camp Nou, the same injury that kept the Brazil international out of three club matches and two international friendlies in October.
The reported injuries come on the day that Spanish club dismissed Julen Lopetegui as manager.
On Monday, Marcelo posted on Instagram saying: "Bad things happen on occasion in our lives for us to find the right direction!!! Difficult moment but Real Madrid always comes back."
Mariano will also sit out at least two weeks with an undisclosed muscle injury.
Real Madrid's upcoming schedule before the November international break include a Copa del Rey match against Mellia, a home game against Valladolid, a Champions League tilt at Viktoria Plzen, and another league match against Celta Vigo.