The injury occurred as Williams, signed as an unrestricted free agent this spring after spending the first four years of his career with the Tennessee Titans, was breaking out of his backpedal in a pass coverage drill. His knee buckled and Williams crumpled to the ground, and was eventually taken from the field on a cart with what Vikings officials immediately surmised as a serious injury.
First-year head coach Brad Childress said Sunday that an MRI examination confirmed the severity of the knee injury.
It marks the second time that Williams, 26, has sustained a serious injury to his left knee. In 2004, he tore the anterior cruciate ligament after starting the first nine contests and missed the balance of the season. He returned in 2005, started all 16 games, and registered career highs in solo tackles (65) and total tackles (83).
The loss of Williams almost certainly means that five-year veteran Dwight Smith, recently signed to a three-year, $6.5 million contract after the New Orleans Saints released him, will join Pro Bowl free safety Darren Sharper in the starting lineup. That may have been the case anyway, since the Minnesota coaches want to get the ballhawking Smith on the field, but Williams had made the competition an interesting one.
Childress on Sunday lauded Williams for the manner in which he had accepted the addition of Smith, noting that the four-year veteran only asked that he be given the chance to compete for the starting job that appeared to be his when the Vikings signed him this spring. There is a chance that the Vikings might have rotated Williams and Smith in the lineup, based on the kind of offense they were facing.
A second-round choice in the 2002 draft, Williams has 273 career tackles, five interceptions, 14 passes defensed, three forced fumbles and three recoveries. The former Stanford star has played in 57 games.
The Vikings likely will place Williams on injured reserve. It is not yet known if Minnesota will seek to add another safety. The top backup now becomes four-year veteran Willie Offord, who is still rehabilitating from 2005 knee surgery.
Len Pasquarelli is a senior NFL writer for ESPN.com.