Defending champion Roger Federer has withdrawn from the Qatar Open with a back injury ahead of his semi-final against Jo-Wilfried Tsonga.
Federer, the number three seed, is on a 20-match unbeaten run.
But he said: "I hurt my back in the second round [against Grega Zemlja] and I don't see any improvement today.
"I've played through two matches in pain and don't think it's the right thing to risk anything more now. It's the only right decision to make."
After playing Zemlja, the 30-year-old Swiss beat Italy's Andreas Seppi over three sets in Thursday's quarter-final.
But Federer added: "I've just been trying to manage the situation really. Back spasms happen and sometimes you can contain them with massage and pain killers.
"But I don't want to drive myself crazy with more painkillers and I need to do what's right to get it better.
"It is only the second time I have pulled out from a tournament and I have never pulled out during a match.
"It's a sad moment for me, the tournament and the fans, but health comes first."
Federer feels "optimistic" he will be fit for the Australian Open, where he hopes to win back the title he lost to Novak Djokovic last year.
He said: "Although it's not very good, it's not crazy bad. I have had bad backs in the past but this is not very good, otherwise I would definitely be playing.
"I feel that without play and with the right treatment, I will get through it in the next few days. That's my personal opinion right now.
"Then of course I have a long journey in front of me going to Australia but I hope maybe midweek next week I should be a 100% again. But that's just guessing."
Tsonga will face world number two Rafael Nadal or fourth seed Gael Monfils in the final.
The first Grand Slam event of 2012 gets under way in Australia on January 16th.
