
ATP officials said the Russian suffered the problems last week as he won the Kremlin Cup in Moscow.
The world number four was replaced in the draw by Spain's Oscar Hernandez.
Davydenko was confirmed on Monday as the fourth qualifier for November's Masters Cup alongside Roger Federer, Rafael Nadal and Novak Djokovic.
Davydenko and Kiefer last played in the second round of the US Open, with the Russian winning in straight sets.