*not
coz he's a titan and he can control his regeneration
He needs sunlight
He had to blend in, so he probably is forcing the limb to not regenerate as well as his head injuries, but hey he met his grandfather xD
Eren now has full control over his body and his titan power. Injuries helps you shift but you have to have the will to transform as well.
If he is Eren... then, why his leg nor regenerate?