Of course, it should be a sure win for them because they should be motivated by their previous victory. United is also doing pretty good in this competition which is also a positive frequency for them to win the match. Their opponent will not be able to resist defeat, because they don't have what it takes.
Manchester United must be able to maintain themselves in a better zone so that they can directly qualify for the round of 16 without having to go through to the play-off round. Likewise with FCSB who are currently in the top eight of the standings but that position is still not necessarily safe if FCSB cannot win at home today so that both teams may play better in order not to lose even though a draw for Manchester United is enough for this match. But Manchester United players seem to still be very hungry for victory in any competition.