Pigeons will lose a lot of feathers if they are caught by predators or hit by a car, most often those from the back and the tail
Sometimes ( they will be unable to fly. However, the feathers will grow back within 6 weeks and if the pigeon is kept safe it will soon be releasable.
These photos show the progress of a young pigeon that had lost her tail feathers:
Starting to grow
If you have rescued a fledgeling collared dove that cannot stand and has a rubbery beak is that it is probably suffering from a calcium and vitamin D3 deficiency also known as Metabolic Bone Disease. This condition is also common in wood pigeons.
Birds with clenched feet and feathers that have not come out of their sheaths (as in the photograph below) often also suffer from Vitamin B2 deficiency...these conditions, and the effect they have had on the baby can be corrected with calcium and vitamin D3 supplement, such as Zolcal D or Calcivet and a vitamin supplement such as Brewers Yeast, so don't let anyone persuade you that it would be kinder to put the baby to sleep. The feet can also be corrected with splints or bandages as can any splaying of the leg.