(REUTERS) - Swiss tennis great Roger Federer said on Wednesday (Oct 30) that he has withdrawn from the inaugural ATP Cup in Australia in January next year so he can spend more time with his family.

The 20-time Grand Slam winner's decision means Switzerland can no longer take part in the men's team-based event from Jan 3 to 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," the 38-year-old, who is currently ranked third in the world, said in a statement.

"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."

Federer had on Monday pulled out of this week's Paris Masters, a day after lifting a record-extending 10th Swiss Indoors championship title in his home town of Basel.

The A$15 million (S$14 million) 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 teams will play in six groups of four for group-stage, round-robin play, with the group winners and the two best second-placed finishers reaching the ATP Cup Finals in Sydney.

Each tie comprises two singles and one doubles match.

Top-ranked Serb Novak Djokovic and world No. 2 Spaniard Rafa Nadal have confirmed that they will play, as has British former world No. 1 Andy Murray.