Anna Kournikova will not be back playing regularly on the WTA Tour before the middle of August and may miss the U.S. Open because of a persistent back problem, said her agent.

The 22-year-old Russian player has informed organisers of WTA events scheduled for the next two weeks at Palo Alto and San Diego that she will not be taking up wild cards, her agent Phil Depicciotto said.

"She won't play the Canadian Open in Toronto (starting on August 11) but, if she's feeling better, may ask for a wild card into New Haven, which starts the week before the U.S. Open," he added.

The U.S. Open begins on August 25.

Kournikova has a chronic sprain of the lumbar spine, a condition which is inoperable.

"Anna is unable to play a consistent tour schedule with her back the way it is now and unless there is a marked improvement, her schedule will remain uncertain," said Depicciotto.

Kournikova is planning to get back on court this week, playing doubles and mixed doubles at a "World TeamTennis" exhibition event in Pennsylvania.

"After this week, she'll know a lot better how she feels," Depicciotto said. "But even if she feels better, she's not in good enough shape to play regular tour events yet."

Since injuring her back at the Australian Open in January, Kournikova has only played a handful of tournaments and last competed at a challenger tour event in Charlottesville in mid-May.

The Russian attempted to play a grass court tournament in England ahead of Wimbledon but aggravated her back injury in practice and was advised to take four-to-six weeks off.