The Erie Zoo's senior Amur tiger Viktor died Saturday morning. 

The cause of death is not known at this time, but it is suspected to be linked to an underlying illness based on his symptoms and age.

He underwent a procedure Tuesday to work on an ingrown claw, get a physical exam and undergo tests on some minor symptoms he started experiencing.

Viktor recently started to show some mild but unusual behavior including lethargy and lack of appetite before he went under, according to zoo officials. They worsened after his exam.

“We make a commitment to ensure that all of our animals live the healthiest and most comfortable lives throughout all stages of their life,” said Dr. Jenna Epstein, head veterinarian for the Erie Zoo. "As a geriatric animal, we had to weigh the risk of sedating Viktor, but ultimately determined it was best for his well being and comfort to move forward with the procedure to remove his ingrown claw and perform the necessary diagnostics. Sadly, despite our best efforts, he ultimately succumbed to what appears to be a preexisting condition. We will be conducting further tests and a necropsy to determine the cause of death."