UEFA.com has the key stats ahead of the quarter-final first legs, with memories of 1999 and a trip to where it all began for José Mourinho with Chelsea FC in Europe.
Manchester United FC v FC Bayern München
• While Bayern beat United in the 2009/10 (4-4, winning on away goals despite a 3-2 second-leg loss at Old Trafford) and 2000/01 quarter-finals (3-1 on aggregate, including a 1-0 victory in Manchester), for United fans meetings between the clubs will always stir memories of the 1999 UEFA Champions League final. Mario Basler gave Bayern a sixth-minute lead at Camp Nou that they held that until added time when United substitutes Teddy Sheringham and Ole Gunnar Solskjær famously turned the game on its head.
• Bayern have visited Old Trafford four times overall and have a record of W1 D2 L1. The two drawn matches came in the 1998/99 group stage (1-1) and the 2001/02 second group stage (0-0).
FC Barcelona v Club Atlético de Madrid
• Barcelona go into the tie seeking a seventh successive semi-final and hoping their greater experience will tell against an Atlético side who were last at this stage in 1997. Yet the Rojiblancos are unlikely to be daunted in their pursuit of a first semi since 1974 given they are one of only two unbeaten teams left in the 2013/14 UEFA Champions League, along with neighbours Real Madrid CF.
• Barcelona have hosted Atlético 105 times in all competitions with a record of 60 home wins, 19 Atlético victories and 26 draws. Their last Camp Nou encounter in the Liga brought a 4-1 triumph for the Blaugrana in December 2012. Radamel Falcao earned Atlético a 30th-minute advantage but the hosts hit back through Adriano, Sergio Busquets and Lionel Messi (2).
Real Madrid CF v Borussia Dortmund
• The clubs met four times in 2012/13, Dortmund prevailing 2-1 at home in the group stage as Robert Lewandowski and Marcel Schmelzer scored either side of Cristiano Ronaldo's strike. In Spain, Dortmund led twice through Marco Reus and Álvaro Arbeloa's own goal, Madrid replying via Pepe and Mesut Özil, although it was the German outfit who finished top of the group, three points above their opponents.
• The teams were reunited in the semi-finals and again Dortmund held sway, Lewandowski netting all four goals – a European Cup semi-final first – in a 4-1 first-leg success in Germany. Late efforts from Karim Benzema (83) and Sergio Ramos (88) set up a frenzied finish to the return match, but Dortmund held on.
Paris Saint-Germain v Chelsea FC
• José Mourinho's first European game as Chelsea manager was a 3-0 win at Paris in the 2004/05 group stage, John Terry heading the opening goal before two strikes from Didier Drogba. The sequel at Stamford Bridge finished goalless.
• That victory in Paris remains Chelsea's sole triumph on French soil while their opponents have played seven times against English sides with the record W1 D3 L3. Their only success came in the first leg of the 1996/97 UEFA Cup Winners' Cup semi-final, a 3-0 defeat of Liverpool FC to set up a 3-2 aggregate win. In the final they lost 1-0 to Barcelona. Three years earlier, PSG had drawn 1-1 at home to Arsenal FC in the last four of the same competition and went out 2-1 on aggregate.