The current Barcelona Femeni side can legitimately claim to be one of the best women's football teams of all time, but one achievement has thus far eluded them: the perfect season.
It can still be done in 2021-22, but they will need to keep winning their remaining games in order to grasp it.
So what is a perfect season and who has done it? GOAL brings you everything you need to know.
What is the 'perfect season' in football?
When a team is said to have completed a 'perfect season', it means they have gone through an entire league campaign without losing or drawing a single game; they have won every fixture.
Generally speaking, in assessing a perfect season, only the primary league competition is considered. A rare achievement, it requires a combination of supreme talent and consistency, as well as a dash of luck on occasion.
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The concept of a 'perfect season' is not exclusive to football and it is a term which is also applied in other sports, including American football, Australian Rules football and so on.
The first leg of the Women's Champions League semi-final between Barcelona and Wolfsburg can be watched exclusively live on DAZN.
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Which teams have done a 'perfect season'?
The number of teams that have achieved a perfect season is relatively low, particularly in the men's game.
Among the teams to achieve the feat are Scottish side Rangers (1898-99) and Hungarian outfit Ferencvaros (1931-32).
Many more teams have passed through entire campaigns undefeated, including the Arsenal Invincibles in the Premier League (2003-04). Their nickname was inspired by the Preston North End team that went an entire First Division season unbeaten in 1888-89.
Antonio Conte steered Juventus through Serie A unbeaten in 2011-12, while Brendan Rodgers masterminded Celtic's unbeaten season across multiple competitions in 2016-17. Steven Gerrard helped Rangers to an unbeaten Scottish Premiership season in 2020-21.
Legendary Romanian side Steaua Bucuresti famously went three seasons unbeaten in 1986-87, 1987-88 and 1988-89, while AC Milan achieved it in Serie A in 1991-92 under Fabio Capello.
Perfect seasons have been a more common feature of the women's game.
Juventus Women completed a perfect season in 2020-21 in a campaign which also saw them win the 2020 Supercoppa Italiana. Barcelona Women went agonisingly close to achieving it the same season, but lost once to Atletico Madrid.
Norway's Asker completed a perfect season in 1998, while PAOK managed it in Greece in 2010-11 then later in 2018-19. Lyon achieved a perfect season in 2014-15.
NSA Sofia have done it three times (2017-18, 2018-19, 2020-21), while Zytlobud-1 Kharkiv won the Ukrainian league in perfect fashion in 2018-19. Lithuania's Gintra Universitetas pulled off a perfect season in 2020 and Albania's Vllaznia did it in 2021-22.
