The Swiss face a US team led by Andy Roddick (ATP 6) and James Blake (ATP 13) – not to mention the best doubles pair in the world, twins Mike and Bob Bryan – when the first round begins in Birmingham, Alabama, on Friday.

In October Federer - winner of 13 grand slam titles and currently the world number two - committed to the first round of the Davis Cup for the first time since 2004, but he pulled out on February 17.

"After my back injury last autumn I didn't have enough time to build up the affected muscles again and fully heal," Federer said on his website. "I will use the coming weeks for further rehabilitation to be sure that I'm fully fit for the rest of the season."

His teammates lent their support: "We know it wasn't an easy decision for Roger to make, but I think it's very important for his career that he make this decision," said Stanislas Wawrinka (ATP 16), the promoted Swiss number one.

Nevertheless many fans were perplexed, with several voices in the Swiss media doubting the extent – or even existence – of Federer's injury, pointing to his excellent performance in the final of the Australian Open on February 1.

Incomprehension

Jakob Hlasek, who played for Switzerland in the epic Davis Cup final against the US in 1992 (which Switzerland eventually lost), told the SonntagsZeitung newspaper he was astonished.

"Federer has been saying one thing for four months – and then he does the opposite! That's what I find hard to understand. It's certainly possible that his back is hurting now, but if that's the case, he hasn't exactly done everything possible to get in good shape," he said.

Claudio Mezzadri, former Swiss Davis Cup captain, also struggled to understand Federer's decision.

"How did he know two-and-a-half weeks before the match that he wouldn't be able to play? He could have travelled and pulled out at the last moment."

Tough choices

But no amount of speculation over Federer's injury will make Swiss captain Severin Luthi's job any easier. Luthi said it would have been tough beating the Americans even with Federer.

"After Roger pulled out we're definitely no longer the favourites," Luthi said. "We're the outsiders, but we're comfortable in this situation. We certainly didn't come here to lose. We're going to do the maximum and try to win this tie."

To do that, Switzerland will have to win at least three of five matches – four singles and one doubles.

Wawrinka will be the first Swiss on court on Friday, facing James Blake.

Wawrinka actually leads Blake 2-0 head-to head, so there is hope for Switzerland there, but who to send out against Andy Roddick in Friday's second match was a tough one for Luthi.

In the end he opted for Marco Chiudinelli (ATP 341) over the better-ranked Stéphane Bohli (ATP 143).

"It's always the same with our team," Luthi said. "We're always ready to change."

Saturday is doubles day and Wawrinka will team up with Yves Allegro (ATP doubles 96) against the Bryans.

Wawrinka and Federer beat the Bryans in the semifinals of the Beijing Olympic Games en route to winning gold, but few people expect another upset.

On Sunday it is the reverse singles: Roddick plays Wawrinka and Blake plays Chiudinelli.

Priorities

The tie will be on a hard court at the Birmingham-Jefferson Convention Complex. The winner advances to the World Group quarterfinals in July; the losers are off until September.

Roddick acknowledges that Federer's absence "took a little bit out of the match".

"It's a weird dynamic because obviously it increases our chances of winning having him not here," he said at a news conference.

However, Federer has also received support, notably from Boris Becker.

"He has to get his priorities straight," he said. "I also once pulled out of the Davis Cup and they almost crucified me in Germany. But I finished the year number one and everyone forgave me."

So it's as easy as that – if Federer finishes 2009 ahead of Rafael Nadal, "Backgate" will be history.

swissinfo, Samuel Jaberg and Thomas Stephens