The draw for the league phase of the Champions League will take place on Thursday evening.
All 36 clubs have been grouped into four pots.
Each club will face eight different opponents — two from each pot.
UEFA restrictions mean there is same-country protection, meaning teams from the same league cannot face each other.
There will also be no identical away fixtures in three consecutive seasons.
Real Madrid cannot face any of Atlético Madrid, Real Betis, Villarreal or Barcelona.
However, José Mourinho’s men are guaranteed to face two of PSG, Bayern Munich, Liverpool, Inter Milan, Manchester City and Arsenal.
Barcelona also cannot face any of their LaLiga rivals but are guaranteed to face two of Inter Milan, PSG, Bayern Munich, Liverpool, Arsenal or Manchester City.
Manchester United will return to the Champions League following a two-year absence.
The Red Devils cannot be drawn against Arsenal, Liverpool, Manchester City or Aston Villa.
United will face two teams from Pot 1, with Real Madrid, Barcelona, Bayern Munich, PSG, Inter Milan and Atlético Madrid among the possible opponents.
UCL draw: Teams that Real Madrid, Man Utd, Barcelona could face in league phase