Carlo Ancelotti's troops lost in the competition for the first time since May 2023 on matchday two, as they were stunned 1-0 by Ligue 1 outfit Lille thanks to a Jonathan David effort.
However, Los Blancos warmed up for Tuesday's Wembley reunion in ideal fashion with a 2-1 La Liga beating of Celta Vigo, one that temporarily drew them level with leaders Barcelona in the top-flight table on 24 points.
Here, Sports Mole rounds up Real Madrid's injury and suspension news ahead of their clash with Dortmund, who obliterated Celtic 7-1 last time out in the Champions League.
Dani Carvajal
Status: Out
Type of injury: Knee
Possible return date: Unknown
Influential right-back Dani Carvajal should not be seen again this season, as the Spaniard is now on the mend from a knee operation to address the severe injury that he picked up earlier this month.
David Alaba
Status: Out
Type of injury: Knee
Possible return date: Unknown
David Alaba has now been sidelined for 10 months with a severe ACL problem, and the experienced Austrian defender is still some way off a return, which may not occur before the end of the year.
Brahim Diaz
Status: Out
Type of injury: Abductor
Possible return date: Unknown
Brahim Diaz sustained a moderately severe abductor problem against Real Sociedad in September, and there are fears that the 25-year-old will not be back on the field until around Christmas time.
REAL MADRID'S SUSPENSION LIST
Real Madrid have no players suspended for this match, although Luka Modric - who became Los Blancos' oldest-ever player at the weekend - is one yellow card away from a European ban.