"I need to ensure I'm ready for the Games and cannot take any risks. I will be ready in August," the former 100 metres world record holder said.
"I've been carrying some soreness in my groin since the Olympic trials and have been unable to train at 100 per cent."
Powell was scheduled to face American Tyson Gay in the 100 metres dash but pulled out as a precaution to save himself for the July 27-August 12 Games.
Two weeks ago, Powell had to be helped off the track after he finished third behind world champion Yohan Blake and world record holder Usain Bolt at the Jamaican Olympic trials.
Last summer, a similar groin injury kept him out of the world championships in South Korea.
His agent said the latest setback was not serious.
"We've just being treating his groin so it heals," agent Paul Doyle said on Thursday.
"He feels fine now, but we've decided to take some more rest, then train, so he'll be ready for the Olympics."
The men's 100m competition begins on Saturday August 4 with the final the following day.