It is understood that the duo, who were both members of last September’s All-Ireland winning panel, withdrew for personal reasons.
St Vincent’s netminder O’Shea made four championship appearances during the 2007 campaign when he deputised for regular goalkeeper Alan Quirke who injured his shoulder and has gained a number of league appearances, including the recent defeat against Dublin in Croke Park.
Carbery Rangers player McMahon, who won an All-Ireland minor medal for Cork in 2000, did not feature for Cork during the 2009 season due to work commitments in Scotland.
But he returned to the squad last year and came on as a sub in the Munster semi-final replay defeat to Kerry.
Counihan will be able to call on the services of dual star Eoin Cadogan for Saturday night’s NFL Division 1 tie against Down in Páirc Uí Rinn, despite the county hurlers facing Waterford on Sunday.
Cork will also have Noel O’Leary back from suspension while Paul Kerrigan and Brian O’Regan are available again after Nemo Rangers’ All-Ireland club exit.
Anthony Lynch, Alan Quirke, Graham Canty, John Miskella and Ger Spillane remain on the injured list.
U21 duo Ciarán Sheehan and Aidan Walsh will be marked absent this weekend as they have been released to prepare with John Cleary’s Cork squad ahead of their Munster U21FC semi-final on March 23.
UCC Sigerson Cup winners Ken O’Halloran, Jamie O’Sullivan and Sean Kiely have all returned to the Cork senior squad after their weekend triumph while four of their college teammates have been drafted onto Cork’s extended training panel. James Fitzpatrick and Kevin O’Driscoll will link up with the squad for training immediately while Mark Collins and Barry O’Driscoll enter the frame once their involvement with the Cork U21’s has come to an end.
Down goalkeeper Brendan McVeigh will miss the Cork clash because of a knee injury. McVeigh sustained a medial ligament tear in the first half of the league win over Armagh.
Benny Coulter could be ruled out again by a hamstring injury while defender Dan McCartan remains unavailable due to a broken finger.
Meanwhile Galway forward Sean Armstrong looks set to miss the remainder of the league after it was confirmed that a hamstring injury picked up in the Sigerson Cup last week will keep him sidelined for a month.
Galway will have to manage without their top scorer in the league with Armstrong, who scored 0-13 in three games, out of action having been injured playing for UL in their Sigerson Cup quarter-final loss to NUI Maynooth last week.
Galway hurling manager John McIntyre sent seven members of his battered squad for cryotherapy treatment on Monday evening as the league champions bid to hold on to their crown when they face Kilkenny next Sunday.
Galway’s biggest worries centre around free-taker Ger Farragher and wing-forward Eanna Ryan, both of whom had to go off with dead legs in the 1-20 to 1-17 loss to Cork.