Great Britain will seek to build on the successes of 2021 when the new men's tennis season begins with the ATP Cup.

Barely a month after losing to Germany in another men's team tennis event - the Davis Cup - Great Britain open against those same opponents.

They are in a tough Group C, which also features Canada and the United States.

Norrie faces world number three Alexander Zverev in his first match on Sunday after British number two Dan Evans takes on Jan-Lennard Struff in the opening singles rubber of the best-of-three tie.

Zverev missed the Davis Cup because he said it was not "the real Davis Cup" and it should not have changed its format two years ago.

That change, coupled with the introduction of the ATP Cup to the calendar in 2020, has resulted in two very similar events being played just weeks apart.

Several top players, including Rafael Nadal and Novak Djokovic, have called for the two events to be merged. Conversations between the ITF, which organises the Davis Cup, and the ATP have been more productive in recent months, as the two organisations consider combining the events.

But for now, we go again as the Russian team seek to defend their ATP Cup title four weeks after also winning the Davis Cup.

What is the ATP Cup?

This is the third edition of the ATP Cup, which features 16 countries competing in four groups at two venues in Sydney - the Ken Rosewall Arena and Qudos Bank Arena.

While there are many similarities with the Davis Cup, in terms of a 'World Cup of tennis' type of event where ties consist of two singles and a doubles rubber, there are also differences.

Qualification for the ATP Cup is based on the ATP ranking of each country's top-ranked singles player, while there are also rankings points on offer.

A player who plays and wins all possible singles matches can earn 750 ATP rankings points. The only events where more points are on offer are at the four Grand Slams (2,000 for winner), ATP Finals (1,500) and nine Masters events (1,000).

The number of rankings points awarded depend on the ranking of the opponent and the round of the result. Doubles rankings points are also offered.

Like at the Davis Cup, the singles matches are best-of-three tie-break sets. But the difference in the doubles at the ATP Cup is that there is no-advantage scoring and a match tie-break instead of a third set.

Each team plays three group matches and the four group winners will advance to the semi-finals.

The nine-day $10m (£7.4m) event culminates in the final on 9 January, which is just over a week before the start of the opening Grand Slam of the year, the Australian Open.

Who is in the Great Britain team?

Great Britain have made one change to the team who played at the Davis Cup Finals, with Jamie Murray coming in for Neal Skupski for the doubles alongside Joe Salisbury.

Liam Broady, who was in the team but did not play, is the fifth member - and also captain - although is once again likely to be cheering on his higher-ranked team-mates in the singles.

Norrie enjoyed a breakout season in 2021, winning the prestigious Indian Wells title and appearing at the ATP Finals as an alternate as well as storming up the rankings, while Evans also had an excellent year, winning his first ATP title.

They are, however, in a tricky group with Canada, boasting world number 11 Felix Auger-Aliassime and 14 Denis Shapovalov.

Germany not only have Zverev, but also Struff, who beat Norrie in the singles in the Davis Cup.

The other team in Group C, the United States, have world number 23 Taylor Fritz as their highest-ranked player.

Who else is playing at the ATP Cup?

While seven of the men's top 10 players will feature at the event, the traditional 'big three' of Djokovic, Nadal and Roger Federer are absent.

It is something tennis will need to get used to.

"I guess that's how it is going to be generally in a few years' time, potentially maybe in three years' time," said world number four Stefanos Tsitsipas, who will be leading the Greek team's hopes.

"So getting used to it earlier, it's pretty much a new reality. Let's see how tennis works out without the top three. I really want to see which players are going to prevail at this point."

Serbian world number one Djokovic withdrew on Wednesday with organisers not giving a reason, Nadal is recovering after Covid-19 and Federer has had knee surgery.

The strongest team on paper is Italy, who have two top-10 players in Matteo Berrettini and Jannik Sinner.

The Russian defending champions are led by world number two and US Open champion Daniil Medvedev, but their team has been weakened by the withdrawal of Andrey Rublev, Aslan Karatsev and Evgeny Donskoy because of positive Covid-19 tests.