Quarter finals draw is based on the Rankings of the team. It is highly unlikely that Manchester United and Chelsea could face each other in Quarters. Semis are not based on rankings though.
POT 1
Chelsea, Barca, Liverpool, Man Utd
POT 2:
Arsenal, Porto, Villareal, Bayern
The draw for semis is Random though. We may end up with any team in the semis cus its random.