EAST RUTHERFORD, N.J. -- For the second time in three seasons, New York Giants starting cornerback William Peterson has a potentially season-ending back injury.

Peterson, listed as doubtful for Sunday's game against St. Louis, said Thursday the injury could force him to miss the game and possibly the rest of the season.

Peterson said the team's medical staff diagnosed a fracture of his lower back after he had an MRI exam last week. He experienced pain while playing against the San Diego Chargers on Sunday night, and said further tests this week showed the injury to be more serious.

"I was told it was something I could play with that would just cause me pain, but it wouldn't cause any other damage to the back," he said. "But after the game, on Monday I was told it was more serious in nature. Right now it doesn't look good for this weekend and it doesn't look good for this season."

The fifth-year cornerback missed all but the first five games of the 2003 season with a stress fracture in his lower back. He said the current injury is similar, but feels worse.

A bone scan performed this week revealed the pain was a result of "hot spots," or evidence of a developing stress fracture, on the other side of the same bone Peterson injured in 2003, according to Dr. Russell Warren, the Giants' team physician. What showed up on an MRI last week was an older fracture that was not the source of the pain.

"Will had a stress fracture in his back two years ago. At that time, we held him out for the remainder of the season and it has not been an issue," he said Thursday. "The bone scan that was administered this week shows signs that he is developing a stress fracture on the other side of the same bone.

"Stress fractures develop over time, typically over months, so it would be difficult, if not impossible, to identify one particular episode as the cause for the stress fracture."

Peterson is scheduled to meet with Dr. Frank Cammisa, the team's spine specialist, on Monday.

"Any time you're dealing with your back, you're not dealing with knees and wrists and ankles, you're dealing with something that can affect your quality of life after football," said Peterson. "So you've got to be careful."

Peterson's injury is a blow to a defense that has allowed 284 yards passing per game this season -- fourth worst in the NFL -- and gave up 485 total yards to San Diego in a 45-23 loss. He will most likely be replaced by second-year pro Curtis Deloatch, who started against Arizona on Sept. 11. Rookie Corey Webster, who has played regularly in nickel situations, missed the San Diego game with a quadriceps injury and is questionable for Sunday.

Peterson, a starter since 2002, missed the Giants' final two preseason games and the season opener against Arizona with a sprained knee ligament suffered against Carolina on Aug. 20. He said he first noticed the back injury during his first regular-season game, against New Orleans on Sept. 19.

"I'm thinking it happened in the first game," Peterson said. "I was feeling more soreness as the game went on, and in the second half there was a lot of soreness and running was difficult."