Chelsea midfielder Michael Ballack is a doubt for Germany's opening two World Cup qualifiers as he is still struggling with a foot injury. Joachim Low's side take on Liechtenstein in Vaduz on September 6 and Finland in Helsinki four days later. The Germany captain, who missed his country's last game, a 2-0 international friendly win over Belgium, with the injury, will join up with the squad as planned on Tuesday, but it remains to be seen whether he will be fit for the qualifiers. A statement on the German FA's official website read: 'The appearance of the 31-year-old midfielder in the World Cup qualifiers against Liechtenstein and against Finland is certainly in question.' Ballack telephoned Low on Friday to tell him the foot injury he picked up in Chelsea's opening game of the Premier League season against Portsmouth was still causing him trouble. The statement continued: 'Ballack will be intensively treated by the DFB's medical department from Tuesday. At the moment it looks like the captain will have to have a longer break from training.'