Talented young forward Colm O'Neill will miss the rest of the Football League and Championship season, following a second scan on his cruciate knee ligament injury.
O'Neill sustained the injury during Cork's 0-16 to 0-13 Division 1 victory over Galway in Salthill on Sunday, March 20.
A statement from the Cork County Board read: "Following surgery in Waterford on Thursday (March 31), it has been confirmed that Cork footballer Colm O'Neill suffered damage to his cruciate ligament in the game against Galway.
"The news comes as a huge disappointment to the Cork team and management, and of course to Colm himself and to his club Ballyclough.
"He will now begin the recovery process. Having suffered the same injury three years ago, Colm is well aware of what lies ahead."
It is cruel luck for the 22-year-old who was used as an impact substitute in Cork's semi-final and final wins over Dublin and Down in last year's All-Ireland Championship.
Cork manager Conor Counihan will have to cope with the injury-enforced loss of O'Neill, which comes on the back of Derek Kavanagh's recent retirement and Paddy O'Shea, Kevin McMahon, Kieran O'Connor and John Hayes' voluntary withdrawals from the panel.
Meanwhile, Counihan has made four changes in personnel to the Cork team for Sunday's league clash with Mayo in Castlebar (throw-in: 2.30pm).
Noel O'Leary will start at centre-back this time around, with Jamie O'Sullivan and Sean Kiely added to the defence in place of Paudie Kissane and Denis O'Sullivan.
Dual player Eoin Cadogan has been repositioned to the left wing, and Nicholas Murphy makes way for James Fitzpatrick in midfield.
The final change sees Donnacha O'Connor take over from the injured Colm O'Neill at left corner forward.
CORK (v Mayo): K O'Halloran; R Carey, J O'Sullivan, M Shields; S Kiely, N O'Leary, E Cadogan; A O'Connor, J Fitzpatrick; F Goold, P Kelly, P O'Neill; D Goulding, F Lynch, D O'Connor.