Olstrum received a one-match ban on Tuesday and his absence will be keenly felt in a match Charlton believes carries huge importance.
Charlton said: “It’s a big game for us, and a big game for Dewsbury as well.
“There’ll be no hanging back; it’ll be full-on from the word go.
“Both teams know how crucial it is, but hopefully with a big crowd behind us we’ll get the points.”
Morrison said: “In our next five games we’re playing against teams that are around us in the league table.
“We need to make sure we get as many points as we can, and if we do that it should cement us in the top half. The flip side is that if you drop a couple of games, you’re in the mix fighting at the other end.”
He added: “It’s a big trip to get to Workington and everybody knows it’s a massive advantage for the Cumbrian sides to be playing at home.
“On top of that they’ve got a quality team and they’re just sitting behind us in the league. They’re going to be very, very tough.”