Gena, a 14-year-old crocodile at the Dnipropetrovsk Oceanarium, has been refusing food and acting listless after eating a cell phone dropped by a woman trying to photograph him last month.
The phone kept ringing inside the crocodile for some time.
Phone owner Rimma Golovko says she wants her SIM card back as it contains her photos and contacts.
The crocodile will be taken to a clinic for an X-ray next week to see if the phone is still there. Medics are considering surgery as a last resort.