Recent reports suggested that Royals owner Anton Zingarevich had expressed a desire to spend big in order to stave off the threat of relegation.
But McDermott has insisted the Berkshire club's budget will not stretch that far, and says he hopes to clarify that fact for the sake of the fans.
"First and foremost I would never sign 10 players in January," he told Sky Sports News.
"We wouldn't even have the budget to suggest we could sign those players.
"The owner actually said we've been looking at 10 players. Well actually we've been looking at hundreds of different players because that's what we do, scouts go out.
"January to January we'll see what we've got budget-wise and what we can do.
"Anyone who comes in January, they've got to be in a position where they can hit the ground running.
"What I don't want is any mixed messages coming out. I knew what my budget was in the summer and my budget was spent. I'm waiting to see what my budget will be in January.
"There isn't a bundle of money to be spent in January and I think it's important that the fans know that because it isn't the case."