If that was the real reason and you have anything concrete even documents or even your own written account see a lawyer. Everyone’s disability is private medical information. Your employer has no right to hear about this unless it’s for work accommodations. If he said it was fine, “ok’d “ time off, offered you the job how did he pull it after hearing about disability. How did he hear ? What was he allowing the time off for if he didn’t know about a disability then ?