That tie is poised at 1-1 as Cristiano Ronaldo prepares to return to Old Trafford, and there is little to choose between Borussia Dortmund and FC Shakhtar Donetsk in Tuesday's other game. However, things are looking desperate for the away sides in Wednesday's fixtures: Valencia CF and Celtic FC needing to make up for first-leg home defeats if they are to forge on to the last eight. UEFA.com gets the lowdown.
Manchester United FC v Real Madrid CF (1-1)
• These teams have met in four previous European Cup ties, with the winners going on to lift the trophy on three occasions. Madrid came out on top in the semi-finals in 1956/57 and the quarter-finals in both 1999/2000 and 2002/03, while United prevailed in the 1967/68 semi-finals.
• José Mourinho's overall record at Old Trafford is W2 D2 L2. During three years at Chelsea FC, his stats against the Red Devils were W5 D4 L1, with the FA Community Shield in August 2007 counting as a draw having finished 1-1 before United triumphed on penalties.
Borussia Dortmund v FC Shakhtar Donetsk (2-2)
• The German club have drawn seven away first legs in UEFA competition and gone through on aggregate six times. The sole defeat came on the only occasion they recorded a 2-2 away draw in the first leg, against Juventus in the 1994/95 UEFA Cup semi-finals; Dortmund were beaten 2-1 in the home return.
• Shakhtar have been victorious on their last two visits to Germany, Fernandinho hitting the opening goal when they won 2-0 at VfB Stuttgart in the 2005/06 UEFA Cup group stage. They beat FC Schalke 04 1-0 in Gelsenkirchen in the 2004/05 UEFA Cup round of 32 to secure a 2-1 aggregate success.
Paris Saint-Germain FC v Valencia CF (2-1)
• PSG have won all 13 UEFA competition ties when they have registered a first-leg away victory. Although they reached the UEFA Champions League second group stage in 2000/01, this is the first knockout round fixture PSG have been involved in since 1994/95, when they made it as far as the semi-finals.
• The first leg ended Valencia's 17-match unbeaten run against French sides. They nonetheless remain undefeated in their last eight trips to France, winning four and drawing four. Valencia's last appearance in the quarter-finals was in 2006/07 when a 1-1 first-leg draw at Chelsea FC preceded a 2-1 home defeat.
Juventus v Celtic FC (3-0)
• Juventus have not lost in Europe since 18 March 2010, when they went down 4-1 at Fulham FC in the UEFA Europa League round of 16 second leg, succumbing 5-4 on aggregate. Their subsequent fixtures have produced eight victories and nine draws.They have won their last four European games, keeping clean sheets in all of them.
• Celtic, competing in the round of 16 for the first time in five seasons, have failed to win in any of their previous nine visits to Italy. Overall their 20 matches against Italian teams have yielded: W5 D7 L8 (W0 D3 L6 in Italy). The most memorable contest was the first, Celtic overcoming FC Internazionale Milano 2-1 in the 1966/67 European Cup final in Lisbon to become the first British club to lift the trophy.