MOSCOW (Reuters) - Former world number one Dinara Safina will not play again this year because of persistent back pain, the Russian said Monday.

"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 (www.dinarasafina.com).

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.

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.

(Reporting by Gennady Fyodorov; Editing by Sonia Oxley)