The Toon sit second from bottom on the Premier League table with only two points from six games and the Dutch defender says that flat performances such as the one in the 2-1 home defeat to Watford on the weekend simply cannot continue.
"I can't talk for other players, but it looks like the confidence is not too good," he said.
"Those types of game (at home to Watford) we have to be winning. We were flat.
"We can't accept it. It is how it is at the moment – but we must change. We all know we can do better than this. But we have to believe more and do better because this isn't good enough at the moment.
"Maybe we do need a break in a game or an early goal. But we definitely need to score more - three times in the Premier League isn't enough.
"There's a lot of work to do. We must stay together and move forward. Let's stay positive though, because it is early in the season, and there's a long way to go. But we can all see and all know that it has to be better."
The Magpies next take on Sheffield Wednesday in the Capital One Cup on Wednesday night.
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