Eden Hazard wore the No.50 shirt for his Real Madrid debut, as a mark of homage to the first moon landing, the UK Mirror reports.
Saturday was the 50th anniversary of when astronaut Neil Armstrong stepped onto the surface and famously declared: "That's one small step for a man, one giant leap for mankind."
The Belgian is currently unable to take the No.7 shirt because it is being worn by Mariano Diaz.
Without an official number confirmed by the club, Hazard was given the freedom to pick an available digit to appear on the back of his jersey, when Real Madrid faced Bayern Munich on Saturday night.
And he went for the No.50 to honour the achievements of Armstrong, fellow astronaut Buzz Aldrin and the crew at NASA.
Real are waiting before they announce Hazard's official shirt number, with Diaz expected to pass up the No.7 and hand it to Hazard.
The former Chelsea forward was unable to convince Luka Modric to part ways with his No.10 shirt, which would have been Hazard's first number choice.