They sat out Wednesday night's 3-2 win over Middlesbrough in the final game of pre-season, with Niall Canavan and Tom Newey deputising.
Mirfin sat out the game after taking a knock on an ankle during Friday's 1-1 draw with a Manchester United XI, while Reid has been kept out as a precaution due to a broken wrist.
"Mirfin turned his ankle against Manchester United. Just to be cautious we went for a scan but he's okay," Knill told the Iron's official website.
"We didn't see the point in pushing him to play against Middlesbrough when we have a game against Derby in the Capital One Cup next Tuesday."