Palace lost 1-0 at Chelsea on Sunday and have now failed to score from open play in 630 minutes of football stretching back to November 6.
The Eagles spurned a series of chances at Stamford Bridge and Vieira said: “I think we did enough to get at least a point. The other side is to look at chances created. Again we created enough chances to score goals.
“The problem is not about that. The most difficult thing is to create chances. It is about scoring, we should score more goals, that is a fact.
“We have quality players who can do that. At the moment it is true that we lost a bit of our confidence. We do not take our chances, we have to keep working on that side.
“When you do not win games you lose confidence, but on the other side you tell the players to look at the performances and the performance today was positive.”
Palace have just one win in seven games in all competitions since the World Cup and they face in-form Manchester United at Selhurst Park on Wednesday.
But Vieira is confident results will improve.
“We did it last year [turned the form around] and we will do it again,” he said.