McGarrahan, who is 6 feet 1, 200 pounds, finished second on the team with 15 special teams tackles last season. He has never started a game in his NFL career, which began after he joined Green Bay as a sixth-round pick in 1998.
The player who was expected to be brought back was Daryl Porter, who was cut by the Dolphins on Sunday, but salary-cap ramifications kept Porter from returning this week.
The problem is that Porter, with four years of experience, is a vested player. And that means 100 percent of his salary would count against the Dolphins salary cap if he were signed this week and waived before the end of the season. If he is signed next week and released before the end of the season, then only 25 percent of his salary would count against the cap.
Porter's preference is to re-sign with the Dolphins, but he may look at other opportunities in the meantime.
McGarrahan becomes the 11th defensive back on the roster, and that's one spot where the Dolphins probably would make a cut if they needed to add another player at a different position at some point during the season.