Blades boss Bryan Robson is expecting a tough test against Cardiff City at Bramall Lane on Tuesday night.
Robson is still unhappy with the defending and is demanding drastic improvements.
He began: "The message is not getting through because we still aren't keeping clean sheets. We are all dissatisfied with the results and the performances aren't good enough.
"We are aiming to be at the top of the league, so I can understand why the fans aren't happy. Everyone is getting frustrated and we must work hard to sort things out."
Bryan feels Saturday's defeat against Southampton was due to the mounting pressure on his players, owing to their disastrous away form this season.
He explained, "We are putting ourselves under pressure at home, because of our away form. We need a solid performance against Cardiff, but it won't be easy."
The gaffer then paid tribute to the visitors' strikeforce, which contains former England international Robbie Fowler and Dutchman Jimmy Floyd Hasselbaink.
He complimented the duo, "They are both top players towards the end of their careers, but they have an excellent knowledge of how to score goals, so we have to be on our guard.
"They are an experienced bunch, so we will have to be at our best to get a victory. We need to establish good platforms to wins games."
