Cormier said he does not yet require surgery, but doctors will monitor how his eye heals. The UFC legend was injured in the second round on an accidental eye poke from Miocic and struggled with his vision for the remainder of the bout.
Miocic won the third of their trilogy via unanimous decision, giving him a 2-1 advantage over Cormier, who has said he plans to retire.
"I'm not interested in fighting for anything but titles," Cormier said after the fight. "I don't imagine there's going to be a title in the future, so that will be it for me. I've had a long run. It's been great."
UFC President Dana White said he expects to see Cormier return to the Octagon, rather than retire.
It's unclear if the eye injury will make it less likely Cormier backs off on his plan to walk away. Cormier said he told referee Marc Goddard he couldn't see out of his left eye after being poked, but the official initially thought the injury came on a punch. Fighters are typically given a delay on unintentional pokes and low blows.
If Cormier is done in MMA, he'll finish with a 22-3 (1) record, with his only losses coming to Miocic and Jon Jones.