I have a chick who is three weeks old today. She/he seems to have stopped developing with just the limited wing feather growth. She/he eats well and plays when not sleeping. Its been cold so hiding in a warm spot seems to be the preference. Should I be concerned that this little one may be ill? Poo seems normal.

This was just taken a few mins ago. Three weeks old today.
This was just taken a few mins ago. Three weeks old today.