Will one of these be celebrating in Madrid in May?

The 2019 Champions League final will be held in Madrid, a city which has dominated the competition in recent years.

Real Madrid have lifted the trophy in four of the past five seasons - and the past three in succession - while city rivals Atletico have appeared in two of the past five finals.

But, after a summer of sizeable change - at Real in particular, is this the year when their monopoly on Europe's biggest club prize is ended?

We take a look at some of this year's key Champions League talking points.

Is this the most open CL in years?

Real Madrid's dominance of the Champions League in recent years reached unprecedented levels last season, when they became the first team to win the competition three times in a row.

No side had even managed back-to-back successes in the competition's current format before Real achieved it in 2017.

That hat-trick of titles came under manager Zinedine Zidane, and with Cristiano Ronaldo as the central on-field character. Both have since departed the Bernabeu.

Football analysts Gracenote assess every team's chances of winning the trophy using their Euro Club Index and, for the first time in three seasons, Real do not start the competition as the most likely winners.

In fact, Gracenote say the Spanish giants' chances of winning have dropped from 30% at the start of 2017-18 to 19.4% this season.

The data also suggests there is now a larger pool of potential champions. Twelve months ago, there was a 69.4% chance of the winner being one of Real, Barcelona or Bayern Munich, whereas that figure now stands at 59.5%.

So who has the best chance of winning this season?

Are Real noticeably weaker without Ronaldo?

Spanish football expert Guillem Balague

The real question now Ronaldo has gone is whether Real have that 'get out of jail free' card that he brought to the table.

The individual quality is there, and manager Julen Lopetegui has added more control and more passing, which can easily mix with their usual and lethal counter-attacking game.

That mix of styles suits striker Karim Benzema - it will give him more responsibility, more touches of the ball, and more shots at goal. He has already scored five goals in as many appearances this season.

And Gareth Bale, who demanded a bigger role, is now able to fill in a lot of the spaces previously occupied by Ronaldo.

But the concern lingers: will they have that extra factor Ronaldo gave them? Although he did not score in last year's semi-finals and final he has made the difference so many times over the years.

Ultimately, a player who was directly involved in exactly 50% of Real's goals in the Champions League from 2009-10 to 2017-18 (105 goals, 27 assists) could well be missed when it really counts.

Did you know? Real are playing in the Champions League for the 22nd consecutive season, the longest run in the history of the competition. They have always made it out of the group stages, reaching the semi-finals in the past eight seasons.

With Ronaldo on board, is this the year Juve make that final step?

Italian football expert Mina Rzouki

Juventus have won Serie A seven years in a row, the domestic double for four consecutive seasons and reached the Champions League final twice in four years, only to be torn to shreds by the Spanish opponents they faced.

Their tactics always versatile, their squad united, the only problem manager Massimiliano Allegri pointed to was that Juve, unlike Barcelona and Real Madrid, did not boast a world-class difference-maker to win in Europe.

Cue the arrival of Ballon d'Or holder Ronaldo.

The Portuguese superstar scored his first two Serie A goals on Sunday, a clear sign he is coming to terms with the league's suffocating style of defending. Paulo Dybala, Federico Bernardeschi and Douglas Costa will be tasked with providing assists and goals.

Juventus sold Mattia Caldara, the youngster set to be the next great Italian defender, to bring back 31-year-old Leonardo Bonucci, another move in the transfer market designed to bring success now rather than in years to come.

Juve are notoriously slow starters under Allegri and have yet to play with fluidity, but they already find themselves top of Serie A with a three-point advantage.

They are expected to challenge for the treble, and reaching the Champions League final is the least that is expected in Turin.

Did you know? Allegri is preparing for his 77th game as a manager in the Champions League, taking him third among Italian coaches with the most games managed in the competition behind Carlo Ancelotti (153) and Fabio Capello (78).

La Liga or Champions League - Messi sparks Barcelona debate

Spanish football expert Guillem Balague

Lionel Messi's speech to Barcelona fans at the Nou Camp in the team presentation this summer made it quite clear they were hurt by their quarter-final loss to Roma last season, when a 4-1 first-leg win was followed by a 3-0 second-leg loss and a painful elimination. There is no doubt he wants to make a major impact this time around.

Former captain Carles Puyol also mentioned that perhaps Europe should be the main priority and an interesting debate started.

Defender Gerard Pique and others in the club responded by saying the league has to be the priority and, if you compete well in that, you have a better chance in the Champions League.

Either way, if Barcelona do not progress beyond the quarter-finals - the stage at which they have been knocked out in the past three seasons - it will be considered a failure.

The squad certainly needed to be improved and they have done that with Arturo Vidal, the Xavi-like Arthur, Malcom and Clement Lenglet.

Messi is happy with the strength and depth of the side, and manager Ernesto Valverde feels he has a team ready to compete on all fronts.

Did you know? Valverde has never progressed further than the quarter-finals of the Champions League.

Who are the most likely English challengers?

BBC chief football writer Phil McNulty

The Champions League is the ultimate goal for Manchester City - and, after failure at the quarter-final stage against Liverpool last season, that desire will be even more acute.

Blues manager Pep Guardiola knows what it takes to win this tournament, City's players will have learned from their experiences and they have every reason to hope this can finally be their year.

Or could Liverpool be the first English team since Chelsea in 2012 to lift the trophy?

Jurgen Klopp's side have a tough group alongside Paris St-Germain and Napoli, but if they make it into the last 16 their devastating attack can do maximum damage. Liverpool have the perfect style, not to mention the power of Anfield, to mount another serious challenge.

Jose Mourinho is another with experience of winning the Champions League and cannot be discounted with Manchester United. They will certainly reach the knockout stage, but it is a stretch to imagine them as potential winners.

Spurs showed their pedigree in outclassing eventual winners Real Madrid in the group stage last term, and five minutes of carelessness cost them against Juventus in the last 16.

They have the capacity to beat any team in the tournament on a given day, but once again they must be ranked as outsiders to win.

Did you know? Guardiola has reached the semi-finals in seven of his nine seasons as manager in the Champions League but hasn't taken a team to the final since 2011.

A surprise package? Or a Buffon fairytale?

Gianluigi Buffon has played in three Champions League finals but is yet to win the competition

For all the dominance of the continent's traditional superpowers, in recent seasons there has been space in the latter stages for some surprise packages.

In 2017-18, Roma and Liverpool made it to the last four, a year after Monaco reached the semi-finals in scintillating style.

Could anyone cause an upset this time?

A totally left-field winner is highly unlikely but, in its own way, PSG going all the way would be a shock.

Despite their lavish spending (Neymar for £200m, Kylian Mbappe for £165.7m), the French club have not made it to the last four in the competition since 1994-95. They failed at the last-16 stage last season, and were eliminated in the quarter-finals in the four years before that.

Should PSG fulfil their undoubted potential and emerge victorious in Madrid on 1 June, it would be a first Champions League success for keeper Gianluigi Buffon, who left Juventus this summer after 17 years at the club.

Alternatively, the trophy could stay in Madrid, even if Real's dominance is ended.

Atletico Madrid's Wanda Metropolitano will host the final, giving their manager Diego Simeone added incentive to add to his achievements at the club.

He has twice guided them to the final, losing on penalties to Real in 2015-16 and coming within a 93rd-minute Sergio Ramos goal of winning it in 2013-14, only to then lose 4-1 after extra time.

With Antoine Griezmann committing his future to the club in the summer, some made them favourites for the domestic title, and Simeone knows what it takes to reach the latter stages in Europe.

Did you know? This is Atletico's sixth consecutive Champions League campaign, the longest run in their history.