Canaries skipper on Tyneside loss
Having trailed 3-2 at the end of a dramatic opening period, a series of counter-attacking goals from the hosts in the second half saw United race to a convincing victory.
Speaking after the game, Martin told Norwich City TV: "They could have opened us up at any point because we weren't good enough.
"It was far too open. At the top end we had some good moments but we've let them create far too many chances.
"They've punished us, which shows the ruthlessness of this league. Newcastle scored easy goals, which is frustrating.
"We looked vulnerable, and it's something we have to put right next week."
The 29-year-old stressed the need to now switch collective focus towards the Canaries' upcoming fixture against West Bromwich Albion, and added: "We can't get too high or too low and will move on.
"There's no crisis but today was not good enough. Nobody can argue if the manager makes changes after this.
"We're hurting but have to get over that quickly. It's our togetherness and working as a unit which makes us a good team, and that's what we need now."