US Open champion Andy Murray has pulled out of the Swiss Indoors tournament in Basle due to a back injury.

The Olympic champion, seeded second behind defending champion Roger Federer, withdrew from the event, which starts today, ahead of a busy end to the season. The Paris Masters, begin a week today, and the Scot will then head to the World Tour Finals in London, which start on November 5.

"There is a fine line between good luck and bad luck," said tournament director Roger Brennwald.

It is the second successive Murray has pulled out of the tournament due to injury. The 25-year-old requested a wildcard to play in Basle a year ago but suffered a strained gluteal muscle just before his opening match against Robin Haase.

Meanwhile, British women's No.1 Heather Watson has said that the disappointment of not being chosen to play the Olympic mixed doubles with Murray has made her stronger.

Murray opted to partner then No.1 Laura Robson, who won a silver medal with the Dunblane man, before reaching the fourth round of the US Open and becoming the first British woman to reach a WTA Tour final – at the Guangzhou International Open – since Jo Durie in 1990.

"Yes, I wanted to play," said Watson. "It was the Olympics. I think anyone in my position would have wanted that opportunity. But it was his decision. It's fine. They ended up with a silver medal – that's brilliant. It's made me stronger."

Watson had won a doubles title just before London 2012, then went one better than Robson by triumphing last Sunday in the Japan Open. The win took the Guernsey-born 20-year-old into the world top 50 for the first time – two places above Robson.