The Wales international pulled out of last weekend's 4-1 win over Getafe with a thigh problem and although Ancelotti expects he will be fit for Saturday's derby against Atletico he will not take any risks.
That means the former Tottenham star is definitely out of Wednesday's trip to face lowly Elche.
"He did not have anything serious. He had a small problem and today he has done individual work," said the Real boss.
"He will be available on Saturday, not tomorrow. He played 60 minutes against Villarreal and played 30 against Galatasaray.
"He just has a small problem, but not a muscle injury. I do not know what happened, but the important thing is that there is no risk if I decide to put him on the pitch on Saturday against Atletico."
Elche have managed just three draws in five matches since their return to the top flight but Ancelotti is taking nothing for granted, especially considering his side's habit of conceding the first goal which has happened three times in the league so far.
"We have talked about this with the players and we agree that we need to start matches with more intensity," he told his pre-match press conference.
"We have always had problems early on and then we improve as the minutes go by. Our aim tomorrow is to start better.
"It will be difficult and we have to be careful with this match.
"We are facing a team who are very keen, who won the league (second division) last season and playing us is a big motivation for them.
"We have to concentrate and have as much character and desire to win as them."
Elche are given little chance against Real but midfielder Fidel Chaves insists they are desperate to record their first win at home.
"We will fight every week for three points. We know Real are one of the best teams in the world but we believe in ourselves," he told elchecf.es.
"We want to get the first win at home. Our fans never fails to make us feel like it's a big party.
"It will be difficult but we will try. Nobody doubts this team, who always compete from the first minute and come out on the attack without compromise.
"We're not going to change the way we play because of the opponent."