Canada's Davis Cup finals hopes suffered a blow when Milos Raonic withdrew from the team on Monday with a back injury.
The 28-year-old former world No.3 will be replaced by 94th-ranked Brayden Schnur for the week-long event in Madrid.
"It is very hard and disappointing for me that I will not be able to represent my country at Davis Cup," Raonic said in a statement issued by Tennis Canada.
"My health has continued to let me down through this entire year and now once again. I will take the appropriate time to get healthy and I look forward to being back on court next season."
Even without Raonic, Canada have a strong squad with world No.15 Denis Shapovalov and fellow youngster Felix Auger-Aliassime, ranked 21st, both making the trip.
Canada are one of 18 nations contesting the first edition of the Davis Cup since its radical revamp. They face Italy on November 18 and the United States a day later in Group F.