But both men believe the world-record signing is ready to start against Barcelona at the Nou Camp on Saturday.
The 24-year-old Wales forward has struggled with a thigh injury in recent weeks but was introduced from the bench against both Malaga in the Primera Division last weekend and against Juventus in the Champions League on Wednesday, and Ancelotti hinted at his pre-match press conference that Bale could start this weekend.
"I'll see what happens in training (on Friday evening) and then I will make the decision to put him in (the starting line-up) or not," the Italian said.
He joked: "It's the fault of the press officer, to organise a press conference at 3pm! I have to do the training and (Friday) is very important to decide. If we had been training before the press conference, you could know.
"It's true that he didn't have an easy time and he's worked hard. He used the (international) break to improve his condition, and, in my opinion and his opinion, he is ready to play from the start.
"He's ready. We're going to see the best of Bale now."
Ancelotti will also have to decide whether to select Alvaro Morata or Karim Benzema, and was not giving much away on Friday.
"Morata is in a better physical shape than Benzema now because Benzema did a great defensive job against Juventus and he's more tired," he said.
"But (on Saturday) we need quality, not just hard work, and experience in these games is also important."
Ancelotti believes the match comes at a good time for his team and has urged his players to show "courage and personality" against Gerardo Martino's league leaders.
A home victory would move the champions six points clear of their arch rivals - a not insurmountable deficit for Real but one which could prove daunting at this early stage of the campaign.
However, fresh from a 2-1 midweek win over Juventus and last weekend's action in La Liga - Real beat Malaga 2-0 while Barca and Atletico dropped their first points this term - Ancelotti appeared quietly confident.
"The timing is good for us," he said. "Last week was good and we improved a lot in all aspects. We can do well. The approach we have is going there to play and show our quality and our game.
"I do not know who is favourite. Everyone thinks Barcelona, but this is not bad for us.
"It is difficult to prepare for this game. Motivation and concentration are massive.
"The key is to have courage and personality to play football, not just defend and wait.
"We need character, personality. You should go to Barcelona and try to play football.
"The most important thing is that we do something positive when we have the ball, link up well and, if we have space for the counter-attack, why not?"
Ancelotti, who arrived at the Bernabeu from Paris St Germain in the summer to replace Mourinho, will be overseeing his first Clasico in Spain - and cannot wait to experience it first hand.
"I've seen many games and the one I liked best was the Barcelona-Real Madrid in recent years," the 54-year-old said. "Madrid have improved a lot - starting badly with Mourinho but eventually achieving good results against them.
"(On Saturday) everyone knows what they have to do.
"It's an important game, but the result is not decisive for the league because it is a long season."
Martino will also be viewing his first Clasico from the dugout after taking up the Barca reins at the start of the season, and Ancelotti expressed his respect for the job his opposite number was doing.
"Coaching Barcelona is not easy, after (Pep) Guardiola and (Tito) Vilanova, but he is doing a good job," the Real boss said.