The 33-year-old is a three-time Grand Slam winner and first fell to world number one and Wimbledon winner Ashleigh Barty in the Wimbledon semifinals.
But three tournaments in the space of a month have worn on her body, forcing her to turn down the Olympics in Tokyo.
"Representing Germany in London 2012 and Rio 2016 as part of the German team have been some of my favorite memories so far," she said in the statement.
"It makes me even more disappointed to accept the fact that my body needs to rest after a few intense weeks behind me. I need to recover before I return to the competition later this summer."
Olympic tennis has suffered several major defections so far.
Among others, Roger Federer, Rafa Nadal, Dominic Thiem, Serena Williams, Simona Halep and Bianca Andreescu have declined.
Sweden's Mikael Ymer has also turned down the Olympics.