Real are 16th in the Champions League standings on 12 points after four wins and three losses from seven games, while Brest are 13th with 13 points. Real and Brest are both guaranteed at least a playoff spot for the chance to reach the last 16.
Ancelotti's side lost 1-0 at Lille in their last Champions League trip to France in October. They are now on a four-game winning streak in all competitions following a 5-2 loss to Barcelona in the Spanish Super Cup on January 12th.
"We were not at our best level yet, but now we're pretty close. Everyone knows exactly what needs to be done and we've improved as a group," the Italian told reporters on Tuesday.
"The individual contributions have also been significant. Especially (Kylian) Mbappe, of course, but we can't forget Rodrygo, (Jude) Bellingham and Vinicius Jr. All of this gives me more peace of mind."
Ancelotti heaped praise on France forward Mbappe, who has scored 21 goals in 31 games across all competitions since moving to Madrid, including three goals and an assist in the Champions League.
"Mbappe took some time to adapt but now he's in great shape. So motivated. He enjoys playing with his teammates, and we're enjoying it," the coach added.
Real could still secure a direct spot in the last 16 with a top-eight finish but they have to overtake Bayern Munich, Borussia Dortmund, Brest, Lille, Feyenoord, Monaco, Aston Villa, and Bayer Leverkusen, who are all ahead of them in the table.
"We are not going to speculate or keep an eye on other teams' matches. We are going to win and see what happens," Ancelotti said.
Teams finishing ninth to 24th go into the playoffs on February 11th to 12th and 18th to 19th. The draw for the two-legged games is on Friday.
"We'll only focus on ourselves. Winning and trying to finish as high as possible. Then, as for the draw, we will see what happens," Ancelotti added.