The Foxes inflicted a heavy defeat on the Magpies, who had to play the second-half with ten men after Isaac Hayden was sent off for a dangerous challenge on Dennis Praet.
The result increased the pressure on Bruce, whose tactics have been questioned by a section of the St James’ Park faithful after winning just one of his opening seven games in charge.
But Bruce accused his players of not showing enough effort and desire at the King Power Stadium on Sunday.
He told talkSPORT: “First of all, you have to do the basics. So we’ll go to work on the training ground.
“We changed [formation] today, but I don’t think today was anything to do with tactics or this, that or the other.
“Certainly, the effort and the desire and whatever you want to call it was not enough when we were up against it with ten men and 3-0 down, you have to show a bit more. We were just so passive.
“We just accepted everything, which is hugely disappointing for me because it’s not what I want to see from a team of mine.”
Newcastle were already 1-0 down thanks to a Ricardo Pereira goal when Hayden was given his marching orders in the 43rd minute.
Click Here: kenzo online españa
But a brace from Jamie Vardy, Paul Dummett own goal and late Wilfred Ndidi strike saw the Magpies drop to 19th place in the Premier League.