Real Madrid must go through the Champions League play-offs and a tie against either Manchester City or Celtic after failing to finish in the top eight despite comfortably beating Brest.
A Rodrygo double and Jude Bellingham's strike secured a win for the reigning champions, who needed a win in France to stand a chance of an automatic place in the round of 16.
But results elsewhere mean Carlo Ancelotti's side must play an extra two-legged tie if they are to defend their title.
Brest also go into the knock-out play-offs in their debut Champions League campaign.
