The Champions League draw will be held in Istanbul on August 26.
Man United are in Pot 2 which means that they could face teams from pots 1, 3 and 4. It's also impossible for them to play against the fellow English sides until the quarter-finals.
Here's a reminder of the confirmed pots without those teams that would need to reach the group stage through the playoffs.
Pot 1: Chelsea, Villarreal, Atletico Madrid, Manchester City, Bayern Munich, Inter Milan, Sporting CP, Lille.
Pot 2: Real Madrid, Barcelona, Juventus, Manchester United, PSG, Liverpool, Sevilla, Borussia Dortmund.
Pot 3: Porto, Ajax, RB Leipzig, Atalanta, Zenit St. Petersburg.
Pot 3 or 4: Besiktas, Dynamo Kyiv, Club Brugge.
The away-goal rule is abolished starting from the 2021/22 season which means that the game will go into extra time if the score is level on aggregate in the Champions League knockouts.