Ellerbe injured his hip in Sunday's 33-20 win over the New England Patriots.
Ellerbe was a major free-agent signing in 2013. He played 15 games for the Dolphins last season and finished with 101 tackles. He will play in only one game this season after he was injured in the first half on Sunday.
"Well, Dannell's a heck of a player, and we were excited about the prospects of him moving back to the [outside linebacker] position and playing as effectively as he could," Dolphins defensive coordinator Kevin Coyle said. "But that's part of the game, and we move on. Like every team in the league does when you have injuries, you have to have people step up and fill in."
"He's a big, physical linebacker, a guy who has been in the league and effective against the run," Coyle said of Sheppard. "We're excited about it."
Miami (1-0) will travel to play the Bills (1-0) on Sunday in a battle of surprisingly undefeated teams.