The 27-year-old, who has been dogged by injury since winning heptathlon gold at the London Olympics last year, said she was still feeling pain in her Achilles tendon.
"It's pain. It's one little bit that's really painful," she said. "When I compress it and when I'm pushing off it it hurts.
"If I had one event to prepare for, then maybe it would have been a bit easier. But having to train for seven events and get all the work done that I needed to get done, it just hasn't happened, unfortunately."
Ennis-Hill, whose left ankle was heavily strapped, threw 48.33 metres in the javelin - her previous best was 47.49 - to finish fourth and also won the long-jump competition.
But she will not decide whether to compete at the worlds in Moscow, which get underway on Aug. 10, until she is certain she can compete for the title. The heptathlon starts on day three.
"I want to be competitive, I don't want to go to just enjoy it," she said. "I want to contend for the gold medal. The standard is not really amazing at the moment but (world champion Tatyana) Chernova's coming into form. I want to be ready."
- Sports & Recreation