Roger Federer has withdraw from the inaugural ATP Cup. Photo: Alexandra Wey/Keystone via AP)

Roger Federer said on Wednesday he has withdrawn from the inaugural ATP Cup in Australia in January next year so he can spend more time with his family.

Federer's decision to withdraw means Switzerland can no longer take part in the nation-based event on Jan. 3-12 and that six more countries will now qualify, based on the world rankings of their top players.

"It is with great regret that I am withdrawing from the inaugural ATP Cup event," Federer, who is currently ranked number three in the world, said in a statement https://www.atpcup.com/articles/event-news/federer-withdraws-atp-cup.

"After much discussion with both my family and my team about the year ahead, I have decided that the extra two weeks at home will be beneficial for both my family and my tennis.

"It pains me to not be a part of the most exciting new event on the calendar, but this is the right thing to do if I want to continue to play for a longer period of time on the ATP Tour."

The $15 million dollar ATP Cup will be hosted in Brisbane, Perth and Sydney.

Eighteen countries qualified for the tournament after a first round deadline in September, with hosts Australia given a wildcard spot.

The six additional nations will be added after the second entry deadline on Nov. 13.

The countries will play in six groups of four for group stage, round-robin play, with the group winners and the two best second-placed finishers across the groups reaching the ATP Cup Finals in Sydney.

Each tie comprises two singles and one doubles match.

Top-ranked Novak Djokovic and world number two Rafa Nadal have confirmed they will play, as has former world number one Andy Murray. 

Reuters