The crest is a deformity, though it might only be small, there's the possibility that the baby has neurological issues. Now, that may be the case, that might not be the case.
If you stay close and keep the baby upright, could you put some wet food in front of him and tap it with your finger? Really see if you can get his interest.
More importantly, try to get some fluids into him, hold him gently and dip the tip of his beak in the water, this will hopefully encourage him to take a sip.
You could get some yolk and mix that with some water, or some nutri drench if you have any, add to the water and try to get him to drink. You could try that to get some vitamins into him.
Not sure if
@Miss Lydia or
@WVduckchick is around and could advise