Winger Dreyer, 27, has not made the trip to Scotland after waking up “feeling unwell”, explained Riemer.
“I had to take the decision with my doctor to leave him back home,” said the head coach.
The opening round of qualifying fixtures pitched Denmark and Scotland together in Copenhagen and the sides could not be separated in a 0-0 draw.
“We play for a World Cup ticket tomorrow,” said Riemer. “And what happened in the first game, what happened in the second game and fifth game is completely irrelevant at this stage.
“To sit in the changing room after and not having secured the ticket for the World Cup because we were having a hangover from a Belarus game, I don’t think that’s possible with top professional football players.
“They know what it’s all about. It’s the big dream for the squad. It’s the big target for the team.
“Steve Clark has done an amazing job over the last 5-6 years with the [Scotland] team, qualifying for the last two Euros. We have a great deal of respect for the opponent tomorrow, but also a lot of belief in ourselves.
“I expect a game tomorrow with two teams that obviously will go for the win, for the big prize and hopefully an entertaining game with two teams that want to win. What I can tell you is that this is a huge, huge fight.”
