Indianapolis Colts running back Vick Ballard was placed on injured reserve Friday, a day after tearing an ACL during practice.
Ballard rushed for 814 yards last season and helped the Colts in their surprising run to the playoffs.
Colts coach Chuck Pagano said Ballard was injured after he planted his foot on the ground and his knee gave out.
Ballard started the season opener against the Oakland Raiders and rushed for 63 yards on 13 carries.
With Ballard out for the season, Ahmad Bradshaw and Donald Brown will assume most of the carries.