Johnson injured his hamstring against Toledo last week, while Richards injured his knee in the season opener against LSU and will sit out his third straight game.
Neither practiced this week.
Johnson is one of the team's best players, and leads the defense with 22 total tackles. Richards, meanwhile, continues to be plagued by injuries. Last season, hamstring, knee and ankle injuries limited his availability and effectiveness.
Miami was hopeful a healthy Richards would help open up the passing game going into this season. In the opener, Richards was injured in the first quarter on his lone reception of the night.