With four already through, UEFA.com eyes the second legs, with positive omens for Chelsea FC and Borussia Dortmund, and Manchester United FC needing a famous comeback.
Chelsea FC (1) v Galatasaray AŞ (1)
While Chelsea lost only one round of 16 tie between 2005/06 and 2011/12, Galatasaray have not won in eight visits to English clubs, drawing three and losing five. Overall their record against English opponents is W3 D8 L7.
Real Madrid CF (6) v FC Schalke 04 (1)
Madrid have lost just twice on the 25 occasions they have hosted German visitors in the Spanish capital, with 19 victories and four draws. The first-leg reverse means Schalke have won only two of their last 14 encounters with Spanish clubs, suffering seven defeats. In 12 away games against Liga sides their record is W2 D5 L5.
Borussia Dortmund (4) v FC Zenit (2)
Zenit have lost all three ties in which they succumbed at home in the first leg, each in the UEFA Cup: against 1. FC Dynamo Dresden in the 1981/82 first round (1-2 home, 1-4 away), VfB Stuttgart in the 1989/90 second round (0-1 home, 0-5 away) and Bologna FC in the 1999/2000 first round (0-3 home, 2-2 away).
Manchester United FC (0) v Olympiacos FC (2)
The English title holders have won all their previous home matches against Greek teams, while Olympiacos have fallen on every one of their 11 trips to England. However, United have mounted a successful fightback just once after a first-leg defeat in the UEFA Champions League. That came when they overwhelmed AS Roma 7-1 after a 2-1 reverse in Italy in the 2006/07 quarter-finals. Furthermore, they have lost the away first leg 16 times in UEFA competition, and on only six of those occasions have they come back to win the tie. When facing a two-goal deficit at Old Trafford they have won three ties and lost four.