The Champions League returns from its winter break this week with the first four games of the knockout stage.
2011 winners Barcelona travel to Bayer Leverkusen for the first leg of their last-16 tie, while Arsenal make the trek to Italian giants AC Milan.
Elsewhere, surprise qualifiers APOEL visit Lyon and Zenit host Portuguese League leaders Benfica.
Read below to see what Sky Sports' Ray Wilkins makes of the matches...
Bayer Leverkusen v Barcelona
It's a shock to see Barcelona 10 points behind Real Madrid in La Liga but they are still the team to beat in the Champions League.
They reinforced their squad in the summer by signing Cesc Fabregas and Alexis Sanchez, but their domestic form hasn't been that fantastic and they lost 3-2 at Osasuna at the weekend.
Pep Guardiola has been deploying a back three this season and perhaps that is a reason for their slight dip.
The biggest problem with that system is when central defenders get dragged into full-back situations and don't like playing there.
When the Dutch national team used a back three, they played with one centre-half called Danny Blind, who was a good sweeper, and two full-backs who didn't mind getting dragged wide.
It worked for them but it doesn't necessarily work for everyone else. Maybe Barcelona need to go back to the defensive four and play the football that they did last season.
Cesc Fabregas has been a real bright spot for them since he moved from Arsenal in the summer. I think a lot of people wondered where exactly he would fit amongst their star-studded midfield but I always thought he would play a significant role.
I anticipate him scoring 20+ goals this season because the timing of his runs into the box from that midfield area is absolutely exceptional. He's very intelligent and playing with tremendous passers like Xavi, Andres Iniesta and Lionel Messi will give him plenty of scoring opportunities.
I saw Bayer Leverkusen play Chelsea in the group stage of this year's competition and even though they beat the English side at the BayArena, I thought they looked pretty average. They are situated sixth in the Bundesliga, 15 points off first-placed Borussia Dortmund, so they are not having a great season domestically.
They have got some experienced players - Manuel Friedrich and Simon Rolfes have been around for a long time - but they will miss 35-year-old Michael Ballack, who has been ruled out of this game through injury.
Ballack hasn't been a regular starter since he returned to the club last summer, but his knowhow in the final stages of the game could have been vital for Leverkusen against such stiff opposition.
They will take some solace from the fact that Barcelona's form on the road has been patchy by their standards - they have only won four of their 11 away games in La Liga - but I would expect Barcelona's exquisite passing to help them claim a comfortable first-leg lead.
AC Milan v Arsenal
AC Milan seem to be a little bit rejuvenated. They got a great result at the weekend, beating Udinese 2-1 away, to move back to the top of Serie A and it's nice to see a side of that magnitude at the top of their league.
I'm sure they will be looking forward to this game because they have hit a bit of form and with Robinho and Zlatan Ibrahomovic up front you would always back them to score.
They also don't rely so much on the old stagers, with the likes of Antonio Nocerino, Alexandre Pato and Kevin-Prince Boateng coming to the fore - even though the latter two may not be rushed back from injury for this game.
Milan won't go gung-ho and will see any advantage they can take to the Emirates as a positive; Arsenal will do well to breach the Italian's defence. However, the Gunners have had success at the San Siro before - they beat Milan there in this competition in 2008 and everyone remembers the Gunners' 5-1 win against Inter in 2003.
I think Arsene Wenger's men will play a counter-attacking game, relying on their substantial pace in wide areas and Mikel Arteta's through balls, because Milan will try to keep possession. Milan do play with a higher tempo on European nights at the San Siro, though, so it should be a very entertaining game to watch.
Arsenal's defence has improved over the course of the season; it will be even stronger once Thomas Vermaelen is back in the centre and the injury to Per Mertesacker may allow him to do that. Laurent Koscielny is playing well and Bacary Sagna's return is a boost.
And then upfront they have the threat of the in-form Robin van Persie and, potentially, Thierry Henry. Wouldn't it be lovely if Thierry finished his second spell at Arsenal with a goal in the San Siro?
Still, I would expect Milan to grab a narrow lead or for the game to end in a draw, leaving it all to play for in the second leg.
The other ties
You would expect Lyon to get the better of APOEL. The Cypriots did brilliantly to top their group and claimed draws in each of their away games at that stage - against Zenit, Porto and Shakhtar Donetsk - but Lyon's extra quality and Champions League experience will probably tell in France.
Benfica looked very good against Man United and top their domestic league, something of a rarity over the last 10 years or so. Midfielder Nicolas Gaitan - a reported target for some of England's major clubs - tops the Champions League assists chart (five) and will be one to watch. Zenit will be hard to beat playing on their own turf, though, and one would have thought it would be extremely cold. This will be a test for Benfica.