The former Tottenham man is likely to have recovered in time to face an Atletico side boasting a 100 per cent record in La Liga so far this season on Saturday night
The former Tottenham man was expected to make his home debut at the Bernabeu against Getafe, but was withdrawn late on with a thigh injury.
Ancelotti will now monitor the Welshman's progress and expects him to have recovered in time for the local derby on Saturday night.
"Marcelo is not available," Ancelotti said at a press conference. "For Bale, we'll wait and see in training if he will be ready.
"I think he will [be ready]. Then I have to make the decision if he will start or be on the bench."
Atletico head into the game with a 100 per cent record to date in La Liga, but Ancelotti believes his side have the greater quality ahead of the crunch clash at the Bernabeu.
"It's hard to say if Atleti are more of a team than us," he said. "They are very compact and play very well. Of course, they are more aggressive than us and have more physical strength, but we have more quality. We are two different teams.
"We'll give our best to win and after the game against Elche I think we'll play with a different spirit."
Los Blancos were awarded a highly-controversial penalty late in the game against Elche in midweek, allowing them to seal a 2-1 win, but Ancelotti pointed to Juan Cala's disallowed goal for Sevilla against Barcelona earlier in the season as proof that officials cannot be expected to get decisions right all the time.
He added: "I think [Saturday] will be a difficult game with a lot of pressure but I don't believe the referee was conditioned like that at Elche."
"I prefer to think that referees, like players, make mistakes on the pitch, nothing more. It is not for me to judge if it was a penalty or not on Pepe or if it was a goal or not for Cala at Camp Nou. Coaches also make mistakes."