( CNN ) -- Roger Federer pulled out of his defense of the Qatar Open Friday with a back injury before his arch-rival Rafael Nadal was beaten in the semifinals of the $ 1 million tournament by Gael Monfils . Federer , the three-time defending champion at the season-opening tournament , was due to face France 's Jo-Wilfried Tsonga for a place in the final . Monfils , who brushed aside top seed Nadal in straight sets , 6-3 6-4 , will now play his compatriot for the first title of the 2012 ATP Tour season . Swiss maestro Federer had nursed back spasms during his wins over Greg Zemlja and Andreas Seppi and undergone treatment between matches as well as taking painkillers . But with the Australian Open looming on Monday week , the 16-time grand slam champion decided against risking the injury against Tsonga . `` I hurt my back in my second round match ( against Zemlja ) and I do n't see any improvement today , '' he told gathered reporters . `` I 've played through two matches in pain and do n't think it 's the right thing to risk anything more now . It 's the only right decision to make . `` It 's 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 sounded a cautious note ahead of the first grand slam of the season . `` Although it 's not very good it 's not crazy bad , '' he said . `` I have had bad backs on the past , but this is not very good , otherwise I would definitely be playing , '' added Federer , who is on a 20-match unbeaten run on the ATP Tour . In the later action on court , a single break of service saw fourth seed Monfils take the opening set . Nadal hit back to lead 4-1 in the second set before Monfils conjured up five games in a row to compete a stunning victory in one hour 36 minutes . Tsonga holds a 2-1 career winning record over Monfils , but he lost their last encounter in Montpellier in 2010 . Earlier , Andy Murray raced into the semifinals of the Brisbane International with a straight sets win over Marcos Baghdatis of Cyprus . World No . 4 Murray beat Baghdatis 6-2 6-2 and will play 19-year-old Australian hopeful Bernard Tomic in the last four in Queensland . Tomic beat Uzbekistan 's Denis Istomin 6-3 7-6 in their quarterfinal match .
Roger Federer withdraws from Qatar Open with back injury . five -time defending champion was due to play Jo-Wilfried Tsonga in the last four . Top seed Gael Monfils lost in straight sets to Qatar 's Gael Monfils in second semifinal . Roger Federer sweeps into semifinals of CNN .