The 25-year-old Bayer Leverkusen star is German coach Joachim Löw's first-choice goalkeeper, but broke a rib in last Saturday's 2-1 defeat to Stuttgart.
The injury throws his World Cup place into question with the tournament set to start on June 11, but Adler is staying optimistic.
"The doctors say the fracture is expected to heal pretty quickly, so I am cautiously optimistic," said Adler, who is set to miss Saturday's Bundesliga clash against Hannover, in a Leverkusen press release on Tuesday.
Adler won the first of his nine caps in October 2008 and along with Schalke's Manuel Neuer and Bremen's Tim Wiese was set to travel to South Africa to battle for Germany's Number One shirt.
Germany have drawn Australia, Serbia and Ghana in Group D and play warm-up matches against Malta on May 13, Hungary in Budapest on May 29 and Bosnia-Herzegovina on June 3.