Ratliff will miss Sunday's game with a high-ankle sprain, which he suffered in the third preseason game against St. Louis. Cowboys coach Jason Garrett said Ratliff has not suffered a setback in his recovery.
Costa hurt his back in training camp and was cleared to start the regular-season opener at the New York Giants. After just three snaps, Costa re-injured his back and was replaced by Ryan Cook. Costa hasn't played since.
"They're both making progress," said Garrett, who doesn't have a timetable on when both players will return. "We're hopeful every week that they continue to make progress and we can get them out on the field practicing. They've done some work on the side at various times, and we want them to return as quickly as we can get it."
"Josh has done a good job," Garrett said of Brent, who has five tackles on the season. "It's always a good test to see how a player who has been in a backup role functions as a starter. He's strong in there, he's instinctive in there and does a good job defending the run and get off blocks. And the more he plays, the better he's going to get. He's really gotten his body in shape. ... We want those big guys to stay big, but the more they play, they have to have endurance, too. And I think he's done a good job with that."