The Magpies are in the bottom reaches of League Two having lost five league games in a row, prompting fans to fear a relegation battle and the possibility of dropping out of the Football League.
Sheridan earmarked the defence as an area that he needs to improve, with County's 34 goals conceded in 20 games one of the worst "goals against" tallies in the division.
"It's not where I thought we'd be. I've got to get a grip of the players," the manager told the Nottingham Post.
"Luckily for me, January is coming. I'll have to make good decisions as we need to get out the position we're in. We can't carry on like this.
"I need players out before I can get any in. That's something I might have to work really hard to do, to reshuffle the back and build a team to win games.
Share your thoughts about this story on Pride of Nottingham by signing up to the website, visiting the forum and joining the conversation.