United will hope the Portugal winger does not emulate Brazil forward Ronaldo who scored a hat-trick when the teams last met 10 years ago.
Berne: The Champions League provides a crackerjack of a fixture on Wednesday when Real Madrid hot-shot Cristiano Ronaldo faces Manchester United, the club where he made his name, for the first time.
United will hope the Portugal winger does not emulate Brazil forward Ronaldo who scored a memorable hat-trick for the Spaniards when the teams last met 10 years ago.
The Real forward will not have to be concerned about being overshadowed by arch-rival Lionel Messi because organisers UEFA have again spread the last 16 over a series of dates, meaning the matches will take one month to complete.
Messi's Barcelona will not be in action until February 20 when they visit AC Milan for their first-leg encounter while the Arsenal-Bayern Munich, Galatasaray-Schalke 04 and Porto-Malaga ties also take place next week.
Another of the group stage's outstanding players, Brazilian playmaker Willian, will not be involved at all as he has joined Anzhi Makhachkala from Shakhtar Donetsk who are at home to Bundesliga champions Borussia Dortmund on Wednesday.
Valencia host ambitious Paris St Germain and Celtic entertain Serie A champions Juventus in Tuesday's ties. The meeting of nine-times European champions Real, who are paying the penalty for failing to win their group, and United is the first for 10 years.
As well as being Ronaldo's first confrontation with the team he spent six glittering seasons with, the first leg at the Bernabeu also allows Real coach Jose Mourinho to renew his rivalry with United counterpart Alex Ferguson.
Real, the Spanish league champions, have been disappointing in La Liga this season and finished second in their Champions League group behind Dortmund. Ronaldo, a United player from 2003-09, will be desperate for his team to rise to the occasion against the club he helped to land the Champions League trophy in 2008.
"I actually said beforehand I believed we would draw United," the 28-year-old told UEFA.com. "I've wanted to face them for some time.
"I have great memories from my time there. They're a team that always do well, every year they're at the top and therefore a team we respect a lot," added Ronaldo who collected his 17th La Liga hat-trick in Saturday's 4-1 win over Sevilla.
The last of the four meetings between Real and United was in the 2002-03 quarter-finals when a treble by Brazilian World Cup-winning forward Ronaldo gave the Spaniards a 4-3 second leg win and a 6-5 aggregate triumph.
Celtic, who beat Barcelona at home earlier in the campaign, and Juventus will clash for the first time since 2001 when the Scottish side won 4-3 in a group game.
Juve goalkeeper Gianluigi Buffon is the only survivor from that match and the Italians have added former France striker Nicolas Anelka to their squad following his move from Shanghai Shenhua.
"Beating Juve would be a bigger step than beating Barcelona. At this stage it would be a massive bonus for us and give us the chance to go to another level of the Champions League," said Celtic midfielder Victor Wanyama.
Shakhtar play Dortmund in Ukraine on Wednesday without Willian who was sold to big-spending Russians Anzhi for 35 million euros last month against the wishes of coach Mircea Lucescu.
The Ukrainians, domestic champions for the last three seasons and Champions League quarter-finalists in 2011, are generally one of Europe's most stable sides and still have eight players from the squad that lifted the UEFA Cup in 2009.
Dortmund are widely perceived as dark horses after topping a group that contained Real, Manchester City and Ajax Amsterdam.
Paris St Germain have not included new signing David Beckham in their squad for Tuesday's match in Valencia, one of four Spanish sides in the last 16, although he is registered for the competition as is fellow new recruit, Brazilian Lucas.