Ryans is out for the season after rupturing his left Achilles tendon in the Texans' 35-31 win over Kansas City on Oct. 17. Cushing has been starting at outside linebacker since the Texans drafted him in 2009.
The Texans had a bye last week, giving coach Gary Kubiak time to consider options for replacing Ryans, who's started two Pro Bowls. Kubiak says he has most confidence in Cushing, who's played in two games since serving a four-game suspension for violating the NFL's policy on banned substances.
Cushing was the Defensive Rookie of the Year last season. He made 133 tackles, including four sacks, and intercepted four passes last season.
The Texans (4-2) play at Indianapolis (4-2) on Monday night.