The French superstar believes he was sidelined by PSG and made to train with players the club were trying to offload after refusing to agree a new contract.
New head coach Xabi Alonso will make his debut on the Real bench for the Group H match at Hard Rock Stadium and could be without several regulars.
Mbappe has repeated his desire to win Europe's biggest club competition, but the closest the Paris-born forward got with his boyhood club was losing the final in 2020 to Bayern Munich.
After the Catalans scraped a comeback win at Valladolid on Saturday, Madrid survived a late Celta fightback to maintain the four-point gap ahead of next Sunday's Clasico.
Mbappe idolised Ronaldo while growing up and after joining Madrid from Paris Saint-Germain last summer, has equalled the Portuguese striker's tally of 33 goals in his first season at the Santiago Bernabeu.
Mbappe's double took him to 33 strikes in 44 appearances across all competitions, the same number of goals as his idol managed in the 2009-10 campaign.
The French superstar did not train with his team-mates on Tuesday ahead of the game but coach Carlo Ancelotti said the striker would travel to San Sebastian.
The Italian coach said that he was never in doubt that the 26-year-old forward was going to find his form despite a slow start in the Spanish capital after arriving from Paris St Germain, playing in a more centralised role up front.
Speaking on a podcast hosted by former Brazil striker Romario, Neymar blamed a clash of egos for the failure of the three stars to gel during their spell together at the French club.
The only time PSG have previously appeared in the biggest match in club football turned out to be a depressingly flat occasion, with the French side losing 1-0 to Bayern Munich behind closed doors in Lisbon in 2020, at the height of the pandemic.
Luis Enrique's team would have sealed the title later on Wednesday if second-placed Monaco had failed to beat Lille at home, but the principality side prevailed 1-0 courtesy of Youssouf Fofana's second-half strike.
Mbappe, who is set to leave PSG in the summer with Real Madrid as the biggest favourite to sign him, told reporters that his future is not in his mind and that his focus is totally on bringing glory to the French capital.
Paris Saint-Germain overcame a controversial first-half sending-off to win 2-0 away to bitter rivals Marseille in Ligue 1 on Sunday, with Portuguese duo Vitinha and Goncalo Ramos scoring their goals.
The Euro 2024 favourites were left reeling after conceding just eight seconds into their game against Germany in Lyon last weekend, which they went on to lose 2-0.
"It is very difficult from a psychological and physical viewpoint to take part in two competitions like that one after the other, in the summer, without having any holiday," Deschamps admitted on Thursday.
"It's very simple, sooner or later, when it happens, we have to get used to playing without Kylian," Luis Enrique told the post-match press conference.
"Mbappe has communicated his decision to PSG but the terms of his exit are yet to be fully agreed. An official announcement is expected once the situation is finalised in the next few months," the report said.
"I was pleased with the whole match, I think my team is competitive each time and today was no exception," said PSG coach Luis Enrique.
Mbappe's contract with the Ligue 1 champions runs out at the end of June and he is free to sign an agreement to join a new club for next season.
