The novelty of single-leg Champions League knockout matches this summer has prompted a lot of discussion among fans about the structure of Europe's premier club competition.
While single-leg knockout games were a feature of the old European Cup, they have made way for a group stage and knockout stage - with two legs each round except for the final - format.
The two-legged knockout tie as we know it, which allows each team the advantage of a partisan crowd, has been in place since the early 2000s, but could UEFA go back to the winner-takes-all approach?
Goal takes a look at why the changes were brought in for 2019-20 and whether they are here to stay.
Will Champions League 2020-21 knockout games be single-leg or two-legged?
Champions League knockout-stage ties will revert to two legs in 2020-21, which will no doubt come as a disappointment to single-leg tie proponents.
Ahead of the 2020-21 tournament, UEFA indicated that Champions League qualifying matches from the first qualifying round to the third qualifying round would be single-leg affairs.
However, the European football governing body confirmed that two-legged ties would return from the play-off round, which was scheduled to get under way on August 22-23.
The round of 16, quarter-finals and semi-finals of the 2020-21 Champions League are all scheduled to be two-legged ties.
Why were the Champions League 2019-20 knockout games single-legged?
UEFA made the decision to change the format of the Champions League knockout stage in 2019-20 due to the extraordinary circumstances of the coronavirus pandemic, which had forced a three-month delay.
In order to complete the 2019-20 tournament in full and in timely fashion, all fixtures from the quarter-final stage on were to be single-leg matches.
The first quarter-final match was played on Wednesday August 12, with the final taking place on Sunday August 23.
Why do some supporters want single-leg knockout rounds?
A number of arguments have been advanced in favour of keeping the single-leg knockout match approach to the Champions League.
Chief among them is the excitement factor, given that each game is a winner-takes-all encounter, which depends on teams being on top form on the day.
Playing a tie over two legs - particularly with the away goals rule - allows teams to adopt different gameplans and can often produce attritional games.
For example, a team could opt to defend resolutely at home in order to avoid conceding an away goal, which would then allow them to play with significantly less pressure in the away tie.
When progression to the next stage relies on a performance and result over the regulation time of one game, teams have little choice but to attack.
Another argument for the long-term introduction of single-leg knockout games is that it can favour ostensibly weaker teams, who may be able to capitalise on strong opponents having an off night.
An example of this came in the Lyon versus Manchester City quarter-final tie in 2019-20, with the French side dumping out a team that had widely been considered favourites to win the trophy.
Had Pep Guardiola's team had the luxury of a second game against Lyon they would have had a second chance where they may have been able to turn things around.
Clubs have discussed the possibility of keeping single-leg knockout matches, according to The Athletic, but the response has reportedly been conservative, with reduced commercial opportunities seen as an issue.
Interestingly, UEFA president Aleksander Ceferin has expressed a preference for single-leg knockout matches.
He told Reuters: “I have to say that this system of one match seems more interesting to me than the other system with two-legged matches, but again it's much too early to say anything about it, let's see."
