The Heineken Champions Cup will see teams from three leagues – Gallagher Premiership, Guinness PRO14 and French Top 14 – battle it out to be crowned kings of Europe this season.

Here, the PA news agency looks at how the competition might pan out and who are the players to watch as the tournament swings into action.

The format

The Champions Cup has increased to 24 teams this season, comprising two seeded pools of 12. Each side plays four group games – against two opponents home and away – in December and January. The top four teams in each pool will secure quarter-final places, with those matches being played over two legs in April. Sides that finish fifth to eighth in each group will form the European Challenge Cup round of 16 alongside eight Challenge Cup qualifiers. The finals of both competitions take place at Stade Velodrome in Marseille on May 21 and 22.

The contenders

European title holders Exeter could again be the team to beat. Their memorable victory over French challengers Racing 92 in last season's final saw them become England's sixth different European Cup-winning club, and they have made a blistering start to the current Premiership campaign, posting three successive bonus point victories. Paris-based Racing again look well-equipped, along with record four-time European champions Leinster and Toulouse, but with just four group fixtures, the margin for error is tiny.

The dark horses

Rugby union's European Cup has been contested for 25 seasons, but the fact that only 12 teams have won it underlines an acute degree of difficulty. Of those former winners, nine are among the title hopefuls this time around, and the bookmakers' odds strongly suggest the champions will come from Leinster, Exeter, Racing or Toulouse. But a host of challengers are lining up behind them, including twice winners Wasps, who were Premiership finalists last season, another double European champion in Irish heavyweights Munster, and perhaps the strongest dark horse of all – Bristol – on their European Cup return after a 12-year absence.

Vive la France!

France boasted the inaugural European Cup winners when Toulouse, inspired by Thomas Castaignede, triumphed at Cardiff Arms Park in 1996. Just two other French clubs – Brive (1997) and Toulon (2013-2015) – have won the tournament since then, but it would be no surprise if they featured strongly this time. The French national team has been revitalised under head coach Fabien Galthie, finishing second in last season's Six Nations and then being beaten by England during extra-time in the Autumn Nations Cup final five days ago. If clubs like Toulouse, Racing, Bordeaux-Begles and current Top 14 leaders La Rochelle can thrive against the back-drop of that feelgood factor, then a first French winner since 2015 could easily materialise.

The players to watch

European Cup rugby has always been a stage for many of the world's leading players to showcase their ability, and this season will be no exception. Fresh from helping England win the Six Nations and Autumn Nations Cup, stars like Jonny May, Henry Slade, Tom Curry and Sam Underhill now prepare for the Champions Cup arena, with Scotland captain Stuart Hogg, Ireland skipper Johnny Sexton, France's Six Nations player of the tournament Antoine Dupont and South African World Cup winners Faf de Klerk and Cheslin Kolbe also among those aiming to make an impression. It promises to be pure box-office.