The Bees were beaten 3-1 on the night at St. James’ Park, with Newcastle dominating the contest for long spells.
Lewis-Potter felt his team did not do enough to stop Newcastle from playing through them.
He stated: “We need to have a bit of nastiness about us.
“We’re expecting to score two/three/four goals every game - we can’t do that. We can’t go into away games expecting to do that and win games, it’s not going to happen.”
He then added: “They score the first one - that’s going to happen in football - but we can’t let our heads drop.
“And we have to be more solid and aggressive from set-pieces, it’s too easy. It’s difficult right now.”
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