What is the format?

After a series of qualifiers in August and September, the four-group, 16-team group stage, first introduced in 2021, starts on Tuesday with German team Eintracht Frankfurt traveling to face Norwegians Rosengard in one of the two early kickoffs.

Two sides will qualify from each group. From that point, two legged ties will decide who progresses right up to the final, a single match at the San Mames stadium, in Bilbao, on May 25 next year.

Who are the favorites?

Holders Barcelona, who provided several key players in Spain's World Cup triumph earlier this year, will again be expected to go all the way to a final in their own country. French side Lyon, who have won 6 of the last 8 titles will also be a threat, even if their standing has dipped slightly.

Beyond those two, Chelsea will be desperate to send off long-serving coach Emma Hayes with the only trophy that's eluded her. Bayern Munich, who must first navigate a tough group including Paris Saint-Germain and Roma, will also be keen to go beyond the semifinals for the first time in club history. The Bundesliga champions are unbeaten domestically this season and added experience and quality in the shape of Magdalena Eriksson and Pernille Harder in the summer.

Who's missing?

The qualification format, which features two different ‘paths' (a champions path and a league path for those who didn't win their domestic title) means several big clubs fall short of the group stage. Last year's beaten finalists Wolfsburg were one of the biggest casualties, after a shock elimination at the hands of Paris FC in the second round.

English sides Arsenal and Manchester United will also be forced to watch from the sidelines after defeats to Paris FC (round one) and Paris-Saint Germain, respectively.

Why is there controversy?

Those absentees have complained about the format, which means that more national champions from smaller federations feature on the big stage at the cost of clashes between the elite teams. In the aftermath of his side's exit, Manchester United coach Marc Skinner let loose: "It's crazy that we have to play PSG in this qualifying round, crazy," he said. "It needs to be something that is addressed. Having said that, we will learn from it. We'll come back stronger. We got a taste of it."

Though Skinner later backtracked somewhat, saying that he meant to suggest there should be "more teams in this competition," PSG midfielder Jackie Groenen also raised an eyebrow. "I think it is a bit strange — big teams going out in the pre-phase," she told the BBC. "I wonder if it's the right way to go."

Though Hayes' Chelsea were one of just four sides to qualify directly (the others were Barcelona, Lyon and Bayern), they have suffered early exits before. "We had to earn that [improvement], over three years,” she said. "Much like how Paris FC had to earn [their group stage entry this year], or whomever for that matter. So, I think we have to respect the format, it's important to say that, we all knew what it was.”

Who are the players to watch?

Ballon d'Or winner Aitana Bonmati is now the key figure at Barcelona and will surely be an orchestrating force once again. Lyon have added one of the World Cup's breakout stars, Haiti's Melchie Dumornay, to a stellar squad that includes the competition's all time top scorer Ada Hegerberg.

Away from the two sides that have dominated the competition, PSG's loan capture of Tabitha Chawinga boosts their goalscoring threat; Lauren James will be looking to build on a promising World Cup with Chelsea; Harder will hope to stay fit in order to add an attacking spark to Bayern; and teenage sensation Linda Caicedo will be key for Real Madrid.

Edited by: James Thorogood