Keller went down with a season-ending knee injury in the Dolphins' pre-season game against the Houston Texans following a hit from DJ Swearinger.
"The loss of Keller is disappointing because he was making so much progress even as a blocker, and then fitting into our offense," Sherman told the Miami Herald.
"The other three guys have really done a nice job. Obviously, they have a lot on their shoulders now with the loss of Dustin, so they need to be able to pick up the slack there."
The Dolphins begin their regular season campaign against the Cleveland Browns on September 8.