Roger Federer has been forced to withdraw from the Dubai tennis championships starting on Monday because of a lung infection, the 16-time grand slam winner said on Sunday.
"I can't play, it's too risky," Federer told reporters. "(It is) a lung infection. It's the first time I've had it. The breathing was difficult. I'm still very tired and a bit slow with everything."
The Swiss aims to return to competition at the World Tour Masters tournament in Indian Wells starting on March 11, but said he would not take any chances after a bout of glandular fever disrupted his preparations for the 2008 season.
That year Federer lost his number one ranking to Spain's Rafael Nadal, reclaiming top spot in July 2009 after winning his sixth Wimbledon title.
"Indian Wells, I hope to be back. Right now, there's no guarantee. I will do tests and see what the doctors say."
The 28-year-old's absence offers Britain's Andy Murray an easier path to the Dubai final, with the duo originally due to meet at the semi-final stage.
Murray will take on Russian qualifier Igor Kunitsyn in Monday's first round as the world number four looks to bounce back after being runner-up at January's Australian Open, his second grand slam final defeat to Federer.
"The Australian Open was great, the whole trip went really well -- I lost to the greatest player of all time in the final and had a few chances," Murray told Reuters on Sunday.
"There are definitely things I can improve on, but I think it was a positive tournament."
Following the withdrawal of Federer and 2008 Dubai winner Andy Roddick, Murray's main threat will come from defending champion Novak Djokovic.