Mayer crashed to the ground in the 110m hurdles of a triathlon organised as part of the Paris Diamond League meeting on Sunday.
He received medical treatment on the track before being helped off, his team later confirming that he had suffered a "significant lesion in his left hamstring".
"It's very difficult to find the words today," Mayer said in a social media post.
"Everything seems unreal since this fall. I was hoping for the chance to express myself in the Stade de France at the Olympic Games. The road seems much longer today."
Mayer, 32, is a two-time Olympic silver medallist (2016, 2021) as well as being a two-time former world champion (2017, 2022) and the current world record holder (9,126 points).
"Count on me to use every minute that separates me from the decathlon to increase my chances of taking part," he added.
The 10-event decathlon at the Paris Olympics is scheduled over two days on August 2 and 3 at the Stade de France.
