Holtby was flexing and stretching his knee after a collision during the third period of Tuesday's home game with the Dallas Stars.
"We're just trying to make sure he's OK," Trotz said. "He's doing fine. You saw, he was moving around fine and took the majority of the shots. Didn't want Stretch in the net."
Copley has a 2.25 goals against average with the Hershey Bears, a .924 save percentage and two shutouts in 41 games. It is the first time this season that the team has had to recall a goaltender.
Holtby has a 3:03 GAA and a save percentage of .906 this season for the Caps, who stand in fourth place in the Eastern Conference playoff seedings with eight games left in the regular season.