"I'm sorry to report that my back is still acting up and I will not be able to play until at least the end of the year," she said on her official website.
The 25-year-old, who has not played since early May, will miss her third successive Grand Slam tournament - the U.S. Open - after also pulling out of the French Open and Wimbledon.
The Muscovite has sounded pessimistic about her return to the main tour.
"I don't know how long my time out is going to last because I don't want to torture myself and my body anymore," the younger sister of former men's world number one Marat Safin was quoted as saying by Russian media earlier this year.
Safina has been criticised for reaching the top without winning a grand slam title, losing all three of her major finals (French Open in 2008 and 2009 and 2009 Australian Open).
After missing much of last year, she made a comeback at the Australian Open in January but suffered an embarrassing 6-0 6-0 defeat by Kim Clijsters in the opening round and soon after contemplated quitting the sport.