The development, which includes 61 apartments facing over the River Lee, is aimed at optimising the value of the hotel's central site off MacCurtain Street, said Gresham group MD Patrick Coyle.
He said the facade, which is listed, and the front section would be maintained and improved.
"There are no immediate staff implications; it is a planning application at present, it utterly depends on what sort of permission we get," he said when asked if the proposed demolition would necessitate the temporary closure of the hotel.
The Gresham Metropole's owners are Precinct Investments, who were among the early consortium bidders on the valuable Jurys Ballsbridge site in Dublin.
Over €4m has already been spent by the group on the 100-year-old Victorian-styled Metropole Hotel.
However, some of this investment will be negated by the just confirmed plans, which currently include the demolition of the leisure centre and swimming pool on St Patrick's Quay.
The owners plan to marginally reduce the Metropole's bedroom tally from 113 to 106 revamped bedrooms, including six penthouse suites in a building of up to seven floors, designed by O'Mahony Pike Architects.
They also seek to build 61 apartments, with one in-fill section rising to twelve floors over basement level and containing only twelve apartments according to yesterday's planning notice, which also lists an 87-space underground car park on four decked levels, as well as five new retail units on St Patrick's Quay and Harley's Street, opposite the Merchants Quay Shopping Centre.
Also biting the dust will be the Metropole's ballroom and other rooms, centres of many late night jazz festival gigs and other functions. They will be replaced with new function rooms of similar capacity, said Mr Coyle.
The Gresham group is investing 6m in its flagship 288-bed Gresham Dublin hotel, the oldest in the city dating back to 1817.
"Both hotels have similar long histories, we are very aware of that, and the Metropole is hugely significant for Cork," said Mr Coyle, stressing the intention to maximise the Cork hotels' site which currently has a large void a service yard in its centre.
The changes mirror the investments being made in existing and new hotels in Cork city centre, and follow a multi-million euro spend on the Imperial Hotel on South Mall.