(CBS) — A three-month-old baby gorilla named Nyambe is in stable condition at the Lincoln Park Zoo hospital after being injured last Wednesday in the enclosure with her mother.

“We’re not exactly sure how that happened, or what happened,” zoo spokeswoman Sharon Dewar says.

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Nyambe suffered a facial laceration. Dewar says she’s “cautiously optimistic” about a full recovery.

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A yell alerted zoo personnel, who put an emergency plan in effect to extract and isolate the injured gorilla baby, Dewar says.

She says the mother had to be sedated to get to the baby.

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Lincoln Park zoo has a dedicated hospital where the gorilla baby is being cared for.