The injury, first reported by The NFL Network and confirmed by team officials, apparently occurred when Hill collided with a teammate. It is believed that Hill broke several small bones in his lower back.
Coach Scott Linehan said Hill was hurt Thursday near the end of
practice and will be re-evaluated next week.
"The best-case scenario is probably two games,'' he said.
Hill, the Rams' top pick in the 2006 draft, knew right away the
injury was serious. It happened when Hill and safety Oshiomogho Atogwe ran into each other on a passing drill.
"I couldn't breathe at first,'' Hill said.
Sixth-year veteran Lenny Walls, a journeyman signed as an unrestricted free agent this summer, likely will start in Hills' place. But the injury leaves St. Louis with just three healthy cornerbacks for Sunday's home game against San Francisco, and if Hill is going to miss an appreciable amount of time, the team might need to sign another defensive back to address the numbers problem.
The Rams' other starter, third-year veteran Ron Bartell, has only nine career starts. Rookie Jonathan Wade, a third-round draft pick from the University of Tennessee, will probably assume the nickel cornerback role.
Fakhir Brown, who started with Hill in 2006 and was projected as a starter again this season, is sitting out the first four games of the season for a violation of the league's steroid and related banned substances policy.
Hill, 25, was the Rams' first-round choice in 2006, the 15th player chosen overall. The former Clemson standout is regarded as a solid cover defender and an aggressive player versus the run as well.
He played in all 16 games as a rookie, starting 10, and had 50 tackles, three interceptions, four passes defensed and a fumble recovery. In last Sunday's season-opening defeat to Carolina, he recorded eight tackles.
Senior writer Len Pasquarelli covers the NFL for ESPN.com. The Associated Press contributed to this report.