McClaren’s side were booed off by the home supporters, and the manager told BBC Sport: “I fully believe in what we are doing. But if we keep playing like that we will go down.”
The 54-year-old added: “There is no flowering it up. Players need to step up and not enough are doing that.
“At the moment I can’t see any positives, but we need to stick together and fight.”
‘The occasion got to some players’
Newcastle’s defeat was their 16th of the season and leaves them 19th in the table with 24 points from 28 games.
It is their fourth home loss of the campaign but their first of 2016.
When asked if Saturday’s defeat was Newcastle’s worst display at St James’ Park under his management, McClaren responded: “Without a shadow of a doubt.
“There was an edginess. We could see that in our players. We played too deep and lost our shape. Some wanted to press as they are encouraged to do by the crowd but the defence did not go with them and it left gaps at the back.
“Normally we are a good attacking team and good on the ball but we were poor on the ball. It is not the level we have produced at home in the last six or seven games. The occasion and inexperience got to a few.”
The home fans at St James’ Park made their feelings clear at the end of Saturday’s game and while McClaren admitted he fully understood their frustration, he insisted he would continue to battle on in his job.
“I’m a fighter and we’ve all got to fight,” he added. “There’s no one from outside the club that can solve it, it’s up to the players and the staff to do it.
“We will prepare to win the next game and put the characters in there who can handle this situation. Whatever happens they will be better players for going through this.”