Roger Federer will return to Davis Cup duty in September when Switzerland will aim to preserve their place in the World Group.

Federer confirmed his decision during an exhibition tournament in Switzerland on Friday.

"He took us all by surprise," Swiss tennis association spokesman Daniel Monnin said in a statement on the association's website.

The world number one sat out Switzerland's first round tie at home to Australia in February, saying that he wanted to concentrate on this year's Grand Slam and Masters Series tournaments and on preserving his ranking.

Despite playing on home soil against an Australian side also without their top player Lleyton Hewitt, the Swiss went on to lose the tie 3-2, setting up September's relegation fight against promotion-chasing Serbia Montenegro.

Federer is set to repeat his strategy from last year, when he was absent from Switzerland's first round defeat to the Netherlands but came back to lead a 5-0 playoff whitewash of Britain.

The Swiss will be at home again for September's tie although the venue and surface for the playoff is yet to be decided.