Neither Houston, who has a toe injury, nor Slay, who has a torn meniscus, have practiced all week.
"It's sort of the conversations we've had with other guys on our roster," Lions coach Jim Schwartz said. "We're confident in all 53 guys, and Jonte (Green) hasn't had to play too much of a defensive role this year. But he did last year, and he's a better player now than he was then.
"So whoever we put out there, we expect him to be able to get the job done."
Green has played 20 defensive snaps this season but started five games in 2012 for the Lions. Greenwood was promoted from the practice squad last week and has not played a regular-season NFL game.
Veteran Rashean Mathis, the Lions' other starting cornerback, is healthy.
Lions rookie defensive end Ziggy Ansah (shoulder) and running back Reggie Bush (calf) are both officially listed as questionable but are expected to play Monday.