* Ibercaja Foundation to sell 40% stake in bank
* Plans are part of legal requirements to be listed in 2022
* Prospectus expected to be approved by supervisor shortly (Recasts, adds detail)
By Jesús Aguado
MADRID, Jan 20 (Reuters) - Spanish bank Ibercaja's biggest shareholder plans to sell about 40% of the lender's shares in an initial public offering (IPO) in February, a source close to the matter said on Thursday.
The IPO, which would be Spain's first this year, is part of legal requirements set under the terms of a bank bailout after the 2012 financial crisis.
"The plan is to be listed at some point during February, potentially around mid-February," the source told Reuters.
Ibercaja, which declined to comment, had earlier announced its intention to float without disclosing a time frame. It would be the first IPO of a Spanish bank since Unicaja's listing in 2017.
The prospectus is expected to be approved by the market supervisor in the next couple of days, the source said.
Spanish authorities had given former savings banks such as Ibercaja until the end of next year to go public or raise money to cut stakes held by foundations.
Ibercaja, which has total assets of 58 billion euros ($65.8 billion), said the offering would be for existing shares held by the Ibercaja Foundation, which currently owns a little more than 88% of the bank.
After completion of the IPO and assuming that an overallotment option of 10% is exercised in full, the Ibercaja Foundation's stake would fall to 46.09%.
The source did not provide any detail on a potential valuation for Ibercaja.
Rival Unicaja trades at 0.61 times its book value, Refinitiv data shows. A similar ratio would give Ibercaja a stock market valuation of about 2 billion euros before any potential discount investors usually demand for such listings.
Rothschild is working as adviser on the proposed IPO, with Morgan Stanley and JP Morgan as global bookrunners. ($1 = 0.8820 euros)
(Reporting by Jesús Aguado Editing by Inti Landauro and David Goodman)