The Detroit Free Press reported that the two players missed the open portion of practice, the part that the media is allowed to watch. Their status is in doubt for Sunday's opener.
The Lions were hoping Delmas would be OK to practice after minor knee surgery about a month ago. Detroit has had special teams captain John Wendling start in Delmas' place all preseason, so that transition should go smoothly.
Houston's absence -- due to a sprained ankle -- means the Lions could go with a three-man rotation at cornerback, including newly signed Drayton Florence. How that group matches up against Rams third-year quarterback Sam Bradford, who doesn't have a big-name target to throw to, remains to be seen.