Lashinda Demus and Brigetta Barrett, two 2012 Olympic silver medalists, will miss the U.S. Olympic Track and Field Trials in July and will not be able to return to the Games in August.
Demus, 33, took silver in the 400m hurdles in London, .07 behind Russian Natalya Antyukh.
Demus, also a four-time world championships medalist in the event, last competed June 28, 2015, finishing fourth at the U.S. Championships.
Since, she has been slowed by plantar fasciitis, vitamin deficiencies, a herniated disc in her lower back that required surgery, a broken right arm and meniscus and PCL tears in her knee, according to a blog post published Tuesday.