But what do their head-to-head records tells us about the possible outcomes? What are the Champions League omens to watch out for? We asked Opta for the lowdown.
Ajax vs Juventus
- Ajax have never beaten Juventus in the Champions League in five attempts (W0 D1 L4) - their last win against them in the European Cup was in the 1973 final.
- Juventus are unbeaten in nine European matches against Ajax (W5 D4 L0) since losing 1-2 in a UEFA Cup match in December 1974.
- This will be the first Champions League knockout meeting between Ajax and Juventus since the 1996-97 semi-final, with Juventus winning 6-2 on aggregate.
- Ajax have played more Champions League matches without winning against Juventus (five) than any other side, while Juventus have only faced Rosenborg (six games) more often without losing than their five games against Ajax.
- Juventus' Cristiano Ronaldo has scored seven Champions League goals against Ajax - only against Bayern Munich (9) and current side Juventus (10) has he scored more often.
- Juventus manager Massimiliano Allegri has faced Ajax four times in the Champions League without winning (W0 D3 L1), facing the Amsterdam side more often without winning than any other opponent in the competition.
Liverpool vs Porto
- Liverpool have never lost a European match against Porto in six games (W3 D3 L0).
- Porto were eliminated by Liverpool in the Champions League last season at the Last 16 stage, losing 0-5 on aggregate.
- Liverpool have lost just one of their 11 home European games against Portuguese opposition (W7 D3 L1), a 0-2 defeat against Benfica at Anfield in the last 16 stage of the 2005-06 Champions League.
- Porto have never faced an opponent more without winning in the Champions League than Liverpool (four games), also failing in four matches against Zenit St Petersburg and Juventus.
- Liverpool have progressed from all four of their European quarter-finals against Portuguese opponents, eliminating Benfica in the European Cup in 1977-78 and 1983-84 and in the Europa League in 2009-10 - their other triumph was against opponents FC Porto in the 2000-01 UEFA Cup.
- Sadio Mane's only hat-trick in all competitions for Liverpool came against Porto in the Champions League in 2017-18 - only Santiago Solari (4) has netted more goals against Porto in the competition.
Tottenham vs Manchester City
- This is the first ever European meeting between Tottenham and Manchester City.
- For the second consecutive season, Manchester City will face fellow English opponents in the Champions League quarter-final - they lost 5-1 on aggregate to Liverpool last season.
- This is Spurs' first European meeting with a fellow English side since the 1972-73 UEFA Cup semi-final, when they lost on aggregate on away goals to Liverpool.
- Manchester City have lost all four of their European matches against English sides, losing both legs of the 1970-71 Cup Winners' Cup semi-final against Chelsea and both legs of last season's Champions League quarter-final against Liverpool.
- Spurs have been eliminated in two of their three European knockout ties against English teams, losing to Man Utd in the 1963-64 Cup Winners' Cup and Liverpool in the 1972-73 UEFA Cup; however, they did win over two legs against Wolves in the 1971-72 UEFA Cup final.
- In all competitions, Manchester City have won their last three matches against Tottenham, with all victories coming in the Premier League.
Manchester United vs Barcelona
- This will be the first European meeting between Barcelona and Man Utd since the 2011 Champions League final, which Barcelona won 3-1 at Wembley.
- Manchester United have never won away from home against Barcelona in any European competition (P4 W0 D2 L2), with this their first match there since April 2008, a goalless draw.
- Excluding finals, Manchester United have progressed from both of their European knockout ties with Barcelona, winning 3-2 on aggregate in the 1983-84 Cup Winners' Cup quarter-final and 1-0 on aggregate in the 2007-08 Champions League semi-final.
- Since their elimination to Chelsea in the 2011-12 semi-final, Barcelona have progressed from all four Champions League ties with English opponents, most recently a 4-1 aggregate victory over Chelsea in the Last 16 stage last season.
- Barcelona have won both of their Champions League quarter-finals against English teams, beating Chelsea in 1999-2000 and Arsenal in 2009-10. o Manchester United have won just two of their last 15 European matches against Spanish teams (D6 L7), failing to beat Valencia in both group stage games this season.
- Barcelona have lost just two of their 41 home European matches against English teams (W27 D12 L2) - both against Liverpool (in March 1976 and February 2007).
- Barcelona's Lionel Messi has scored 22 Champions League goals against English clubs; more than any other player in the competition. He has scored twice against Manchester United in the competition.
- This will be Ole Gunnar Solskjaer's first match as a player or manager at the Nou Camp since the 1999 Champions League final, in which he scored the winner in stoppage time.