ESSENDON will be without one of its most exciting young prospects for the NAB Cup with emerging defender Michael Hurley undergoing an operation to remove his gall bladder.

Hurley, 18, was revealed to have a non-functioning gall bladder after a series of recently conducted tests.

It was removed by keyhole surgery on Friday.

The gall bladder is a non-vital organ that aids in the digestive process by concentrating bile in the liver.

The young backman had been feeling unwell before being diagnosed and undergoing the common procedure.

Essendon believes its No.5 selection from last year's NAB AFL Draft will recover from the operation within a month.

He is expected to miss most, if not all, of the NAB Cup.

The Bombers' pre-season competition kicks off on February 13 against the Western Bulldogs in Darwin.