With Schalke needing a miracle to overturn a 6-1 first-leg deficit and deny Madrid a quarter-final berth, Ancelotti could have been forgiven for focussing his attention on Sunday's Clasico showdown with Barca, where a win would put Madrid seven points clear of the defending champions.
However, while the Italian is planning to ring the changes on Tuesday, he insists he will still treat Schalke with respect and revealed that Ronaldo - who scored a competition-record nine goals in the group stage and also notched twice in the Veltins-Arena last month - will start.
He said: "We will make some changes because on Saturday we had a game that took a lot out of us physically (1-0 win at Malaga), we've travelled and we've not rested much.
"In order to help everyone recover well we will make some changes. Some players will be tired and therefore they won't play."
Although he did not reveal his full starting XI, Ancelotti did confirm his attack, saying: "I can say the three strikers. (Alvaro) Morata, Jese and Cristiano Ronaldo."
Madrid go into Tuesday's game on the back of a 30-match unbeaten streak in all competitions and Ancelotti wants to see that form continue.
He said: "We have to play a good game, it's an important Champions League match and having a good game against Schalke is the best way to prepare for the Clasico.
"Having a good game gives us more confidence. We need to respect our work, the competition and the opposing team."
A much-changed Madrid line-up does not necessarily mean a weakened one, though, with Ancelotti acknowledging the quality in his squad runs deep.
Asked if it was the best group of players he has ever had at his disposal, the former Chelsea, Paris St Germain, AC Milan and Juventus boss said: "It's difficult to make a comparison because I've had squads with a lot of quality, but this squad had a little of everything.
"It has experience, youth, character, personality. In that sense it could be the most complete squad I've had."
While Madrid can expect to take their place in the last eight and continue their hunt for the treble this season, Schalke are realistically only playing for pride and honour at the Bernabeu.
The Bundesliga outfit are determined to go down fighting though, with attacking midfielder Julian Draxler saying on his club's website: "This is a stadium all footballers dream of playing in at least once, even if it's going to be strange given the situation we are in.
"We are all realistic enough to know that we can't get much after losing 6-1, but we still want to play a good game."
Striker Klaas-Jan Huntelaar, who is doubtful due to a calf strain and may not feature against his former side, added: "We want to show we have every right of being among Europe's best 16 clubs.
"Madrid have a great squad and even if they rotate their side, you hardly notice any difference in quality. But if we resist as a team, then I'm convinced we can get a decent result."