The Spanish giants did not name the French superstar, the team's top goalscorer, in their squad on Tuesday for the tournament in Jeddah, Saudi Arabia.
Gonzalo Garcia bagged a hat-trick for Real Madrid as they beat Real Betis 5-1 on Sunday to stay on La Liga leaders Barcelona's tail.
Xabi Alonso said he hopes Kylian Mbappe will be back to take part in the Spanish Super Cup, with Los Blancos facing rivals Atletico Madrid in the semi-final on January 8.
Real Madrid forward Kylian Mbappe has injured his left knee, the Spanish club said on Wednesday. Madrid said in a brief statement the France superstar had been diagnosed with a sprain but did not provide a timeline for his recovery.
Kylian Mbappe matched Cristiano Ronaldo's club record for goals in a calendar year and Jude Bellingham also scored as Real Madrid beat Sevilla 2-0 on Saturday in La Liga.
A Kylian Mbappe brace helped Real Madrid avoid an upset at third-tier Talavera as Xabi Alonso's side scraped home 3-2 to stamp their ticket into the Spanish Cup last 16 on Wednesday.
A Paris labor court has ruled Paris Saint-Germain must pay more than 60 million euros ($70 million) to Kylian Mbappe in a dispute over unpaid wages and bonuses linked to the end of his contract before his 2024 move to Real Madrid.
Kylian Mbappe and Rodrygo Goes's goals earned Real Madrid a tense 2-1 win at Alaves in La Liga on Sunday to potentially keep coach Xabi Alonso in his job.
Kylian Mbappe remained an unused substitute against Manchester even as Real Madrid lost the Champions League match 1-2.
Manchester City came from behind to beat Real Madrid 2-1 on Wednesday in the Champions League and leave Xabi Alonso's position as coach of the Spanish giants in grave danger.