Cushing, who leads the NFL's third-ranked defense this season with 29 tackles, was placed on injured reserve by the Texans on Wednesday while eighth-year veteran Ruud was brought in and kick returner Trindon Holliday cut.
The 29-year-old Ruud had four consecutive 100-tackle seasons for the Tampa Bay Buccaneers from 2007 to 2010, ranked fifth in the league in 2008 and joint second in 2009.
He had 57 tackles and an interception for Tennessee last season before being placed on injured reserve with a groin injury. Ruud signed with Seattle in April, was traded to New Orleans in August and released by the Saints two days ago.
"He's a veteran who's been in systems somewhat similar to what we do," Texans coach Gary Kubiak told reporters about Ruud. "It gives us a little bit of flexibility going into game day."
Cushing, the Texans' most valuable player in 2011, tore knee ligaments in Houston's 23-17 win over the New York Jets on Monday and will have surgery in two-to-three weeks.
Holliday had returned three kicks for touchdowns during the preseason but was averaging 9.2 yards on punt returns and 19.4 on kickoff returns this season. Houston rank last in the league with 17.6 yards per kickoff return.
"By no means is it a statement to what we thought of Trindon," Kubiak said. "We have not been playing up to par on special teams, giving returners the opportunity." (Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Frank Pingue)
- the Texans