Hurd injured his left ankle in the preseason finale and missed the first three regular-season games. The third-year receiver reinjured the ankle Sunday and had surgery this week.
The Cowboys filled the gap left by Hurd by signing free-agent linebacker Carlos Polk. Polk spent seven seasons with the San Diego Chargers until being released at the end of training camp this season.
Polk was with the Chargers when Cowboys coach Wade Phillips was San Diego's defensive coordinator from 2004-06.
"He's a special teams guy that can play defense," Phillips said.
Kevin Burnett, a nickel linebacker and special teams player, missed practice for the second straight day Thursday because of a calf injury. If Burnett can't play Sunday at St. Louis, Bobby Carpenter will likely take over Burnett's role on defense.
Pro Bowl safety Roy Williams, who missed four games because of a broken arm, was a full participant in practice for the second straight day and should play Sunday.