The Blades manager, who will be without Oli McBurnie at home to Coventry City on Saturday, and has a doubt over goalkeeper Robin Olsen, will push for signings in January but does not know if he will get them.
"I believe this team needs three players in three different positions to find some more of the balance and to be more competitive," he said.
"I don't have any assurances, but my position is clear from. Without mentioning specific names, I believe we need to cover these positions.
"I don't have any assurances, but it's not a question of assurances, it's about being prudent and understanding what we need to lift ourselves, our performances and our club too to the highest level."
Asked if he will have to sell to buy, he replied: "In general I am thinking more about adding the players we need than selling anyone.
"It depends on the market and different situations.
"At the moment I don't have any information about huge interest in my players from anyone else. The possibility always exists but we don't have any offers coming to me or any information that people want to pay some money for my players."
Goalkeeper Olsen is a doubt for Saturday's early kick-off, and McBurnie is in Covid isolation.
Ben Davies, Rhys Norrington-Davies and Sander Berge are all back in training, though the latter pair may need more work to be considered match-fit.
"We have a situation with Robin Olsen, he’s come in with a muscle problem and we are assessing him," said manager Slavisa Jokanovic. "We’ll see if he’s available or not.
"Oli McBurnie had some close contact with a person with Covid and is in isolation and cannot start working with his before next Friday."