Wayne, at Frank's age Marek's disease (herpesvirus) is the most important differential diagnosis for a paretic (weak) or paralyzed leg in a chicken. Careful exam of that leg from Frank's toes to his hip should be performed but his not complaining when you've looked at it doesn't support an injury. Please review this link and let me know if you're seeing any other symptoms of Marek's disease: http://www.birdhealth.com.au/#!mareks-disease/c1qzk
You're welcome. Marek's can cause most every symptom imaginable. An atonic crop is possible but not present if Frank's vagus nerve isn't affected in the disease process. Her weakness isn't likely to be of a dietary origin if you're feeding a high quality laying formula. There's no treatment for Marek's. Some chickens will recover; most progress to life-threatening paralysis and are culled. Some suffer peracute (sudden) death. There's no reason to quarantine her because your entire flock has already been exposed and either immune (if vaccinated at 1 day of age, in particular), or carriers of this virus and may or may not ever become clinically ill. Let's see how she progresses. I can't set a follow-up in this venue so please return to our conversation - even after rating - with an update at your convenience. You can bookmark this page for ease of return.
Thank you for the photo, Wayne. That one leg forward posture is strongly suggestive of Marek's. Thank you for your kind accept. I appreciate it.