Manchester City had come from behind to beat Club Brugge to squeeze into the play-offs and they will now need to overturn a first-leg deficit in the Bernabeu if they are to advance any further.
Celtic, who like City, are among six sides to trail by a single goal heading into next week, will also face a huge challenge to overcome six-time European champions Bayern, if they are to progress.
Of the other British clubs, Aston Villa, Arsenal and Liverpool have already booked their place into the last 16, having automatically qualified in the top eight of the league phase.
These are the teams in each stage:
Last 16: Liverpool, Barcelona, Arsenal, Inter Milan, Atletico Madrid, Bayer Leverkusen, Lille, Aston Villa.
Knockout phase play-offs: Atalanta, Borussia Dortmund, Real Madrid, Bayern Munich, AC Milan, PSV, Paris St-Germain, Benfica, Monaco, Brest, Feyenoord, Juventus, Celtic, Manchester City, Sporting, Club Brugge.
