The 6-2 demolition at the ground where the former Hoops defender enjoyed so much success as a player has exposed just how much work he needs to do with the side he inherited from Peter Houston.
But McNamara insisted he did not need Saturday's capitulation to underline that, though United have won against Rangers and Hearts since he stepped into the hot seat at the start of the month, there remains a need for improvement.
He said: "They have to bounce back and they have to stand up and be counted. There are things we know we have to improve on.
"You have to defend properly, and they didn't at times."
McNamara is handicapped by the lack of time he has to spend with his players on the training ground as the games come thick and fast.
But the ex-Partick Thistle manager plans to use every available minute before heading to Fir Park to get his message across.
"We've got to lift them because we have got a big game against Motherwell," he said.
"But we need to defend better as a team. At times they let it become individuals rather than be a back four.
"We are capable of scoring, we have tested Fraser Forster and missed a penalty to make it 2-2. So, it is a thin line sometimes."
McNamara was pleased with the way his side started but admitted the final score line hurt.
He added: "Some of the defending I thought lacked belief later on – they just wanted it over."