Champions League: 8 things you might have forgotten already happened this season

Laurens: Real Madrid favourites vs. PSG (1:46)

Gab and Juls discuss PSG's clash with Real Madrid in the Champions League round of 16. (1:46)

Two-and-a-half months since a ball was last kicked in the competition, the Champions League returns this week as the 2021-22 knockout phase gets underway.

Paris Saint-Germain are set to face Real Madrid, and Sporting CP will host Manchester City as the round of 16 kicks off with a stellar doubleheader on Tuesday, with the first legs of six more weighty continental ties to follow over the course of the next eight days.

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It has only been 10 weeks since we last dabbled in Champions League action, but life moves pretty fast, so it's worth having a refresher on some of the main plot points to have emerged during this season's competition so far.

The group stage was awash with talking points and memorable moments, so here is our pick of the bunch.

Wait, where are Barcelona?

Barcelona failed to make it through to the knockout phase of a Champions League season for the first time in 17 years after washing up in third place in Group E. After scoring just two goals in their first five group games, their grim fate was sealed in their final game when a 3-0 defeat against Bayern Munich ensured that Benfica went through in second place thanks to their own 2-0 win against Dynamo Kiev. Barca had been an ever-present in the knockouts since 2003-04, when they didn't qualify for the Champions League at all, but will now have to make do with a playoff against Napoli for a place in the Europa League's round of 16.

All hail Haller

There is an unlikely name perched atop the 2021-22 Champions League goal chart as we enter the second phase of the tournament. Ajax centre-forward Sebastien Haller is leading the pack with 10 goals from just six games having outscored the likes of Robert Lewandowski (9), Mohamed Salah (7) Cristiano Ronaldo (6) and Lionel Messi (5). Haller became only the fourth player in history to score in his first five Champions League appearances, amassing an astounding nine goals in the process to break the record of eight set by Erling Haaland in 2019. The one-time West Ham United flop began his Champions League career in style by scoring four goals in Ajax's opening group game against Sporting CP, thus becoming the first player to score a quadruple on his competition debut since Ajax and Netherlands great Marco van Basten in 1992.

Ronaldo's late shows

While not quite as prolific as Haller, Ronaldo has a perfectly respectable tally in 2021-22 with six goals in five games for Manchester United. The Champions League's all-time top scorer has made a habit of leaving it late this season, with his 95th-minute winner against Villarreal sealing United's first victory of the group stage before his 81st-minute strike against Atalanta completed a memorable comeback victory. Ever the showman, the Portugal forward then returned to snatch a dramatic 91st-minute equaliser in the return fixture against Atalanta before also scoring in the 78th-minute in a 2-0 win at Villarreal in United's penultimate group outing. Soccer's "Mr Clutch," indeed.

One proud father

Speaking of United, there were touching scenes in December brought about by an 89th-minute substitution in the Red Devils' final group game against Young Boys. An 18-year-old youngster by the name of Charlie Savage entered the fray to make his senior debut for United and just to cap off that special moment, his father -- former United midfielder Robbie Savage -- was on commentary duty.

New Sheriff in town

The most shocking result produced during the 2021-22 group stage was undoubtedly the minor miracle that Moldovan minnows Sheriff Tiraspol pulled off at the Bernabeu in September. The upset came in the 90th minute when Luxembourg international Sebastien Thill found the top corner to spark scenes of pure, unbridled pandemonium in the Spanish capital. Champions League debutants Sheriff held out to beat the 13-time European champions on their own pitch, even going ahead twice on the night before seeing out a famous 2-1 victory.

Thiago's pure connection vs. Porto

There have been plenty of high-grade goals scored in the Champions League already, but the most aesthetically pleasing of them all must surely be Thiago Alcantara's graceful strike against Porto. The Liverpool midfielder made a sumptuous connection with a loose ball to send a sweet 25-yard shot fizzing past Diogo Costa -- a goal that truly gets better with every view.

Draw disorder

We witnessed some good old-fashioned farce back in December when a "technical problem" forced UEFA into an unprecedented re-do of the draw for the Champions League round of 16. The initial draw was declared void after the software meant to guide the UEFA officials throughout the process malfunctioned and began producing ties between clubs that were against competition rules.

Issues arose when Villarreal were drawn against Manchester United, despite UEFA rules stating that two teams who faced each other in the group stage cannot then face each other again in the first knockout phase. This led to a redraw for which United were accidentally left out of the pot entirely before similar errors were made over an illegitimate tie between Liverpool and Atletico Madrid.

After seeing the live draw descend into farce amid administrative disarray, UEFA finally bit the bullet a couple of hours later, scrapped their first attempt and had another go -- much to the chagrin of many interested parties.

No away goals

As the knockout phase whirs into life, it's worth remembering that the away goals rule will not be used in UEFA club competition after being officially abolished last summer. The away goals rule had previously been used in UEFA knockout games since 1965, but now all two-legged knockout ties that are level on aggregate after the second game will simply go to extra time and penalties.