There are some massive Champions League clashes in store this week, but some teams have a far better chance of progression than others.
Some sides might be considered a big deal in their domestic league, but when it comes to the Champions League, they don't have the pedigree to compete amongst Europe's elite.
Here, we will take a look at three sides that need to raise their game if they want to remain in the Champions League beyond the round of 16.
Arsenal have faltered in recent weeks. A 5-1 demolition at the hands of Liverpool was followed by a goalless draw against Manchester United.
Slowly, the Gunners' lead at the top of the Premier League has been eaten up, and they could drop to third place if Manchester City win their game in hand.
With two games against European champions Bayern Munich on the agenda, Arsenal have a lot to prove and will need mature experiences from some of the star names that have not been performing in recent weeks, such as Olivier Giroud and Mesut Ozil.
Bayern will bombard the Arsenal goal, knowing that they conceded five goals against Liverpool and six against Manchester City.
This is the same Bayern team that beat Barcelona, 7-0, over two legs in last year's Champions League semi-finals. In fact, it is probably better now than it was then!
Arsene Wenger's side beat Bayern, 2-0, last season, but only after losing the first leg, 3-0. Now is the time for Arsenal to stand up and show what they are made of. As reported by BBC Sport, Wenger has talked about character and mental strength; now they must prove it.
Manchester City didn't get the luck of the draw. After making it past the Champions League group stage for the first time in their history, they were handed two dates with Barcelona.
Manuel Pellegrini's side could not have had it much worse, and they go into the tie without top striker Sergio Aguero due to injury, just to make matters worse.
At one stage this season, City were awesome. They were scoring for fun and broke the record for the quickest team to score 100 goals in a season, per Sky News' Nick Powell.
But since the turn of February, the goals have dried up a little, and City have begun to struggle. They must quickly recapture the fearless form exhibited earlier in the season if they are going to overcome a Barcelona side who has been there and done it in this competition.
Pellegrini has a chance to show how far he has taken City in a short space of time, but he has struggled against them in the past, as shown by WhoScored:
Against a Barca side whose success in Europe is unparalleled, they will have to be at their very best.
David Moyes' side have just returned from a warm-weather break in Dubai, which was aimed to take them out of the firing line after a disastrous run of form in the Premier League.
Whatever way you want to dress it up, a point against bottom of the league Fulham and a defeat against Stoke City is exceptionally bad for United.
They look to have secured the long-term future of Wayne Rooney, as reported by David McDonnell at the Mirror, but Moyes must get the England international and Robin van Persie back into form quickly before their Champions League tie against Olympiacos.
The Greek side is not one that would usually strike fear into the heart of United, but then again, nor is West Bromwich Albion, Sunderland or Newcastle United, but they have all beaten Man Utd this season already.
They cannot afford to rely on their reputation, and a humiliating exit from the Champions League would turn the pressure up on Moyes and United even further.
Michael Owen agrees with this sentiment:
Olympiacos are confident and used to winning, sitting 20 points clear at the top of the Greek League, and they cannot afford to be underestimated.