The Senegalese striker missed an easy chance to give the struggling Red Bulls a win against New England Revolution last weekend and has come under fire for the error.
But Angel is confident of Kandji's ability and believes he will bounce back.
"I know his ability - and I'm talking just about myself - he has great talent, great ability, but he has a lot to learn and a lot to work on,'' said Angel, the captain and leading scorer with nine goals. "It's up to him how much he wants to progress in his weak aspects of his game, his finishing his alertness.
"He's very good with the ball, he can take people on, he's a good athlete
"We want to make him more complete, want him to be more clinical, to be more efficient in the areas we need him to be better. Obviously it's up to him at the end of the day how much he wants to learn, and about his work ethic and his discipline and his responsibility.''