MADRID, Oct 3 (Reuters) - Spain’s Unicaja and Liberbank are holding informal talks about a potential tie-up to create the country’s fifth-biggest lender with over 100 billion euros in total assets without having entered so far into formal negotiations, a source with knowledge of the matter said. “Informal talks between the two lenders are taking place,” the source said, adding that it was too early to say if that would lead to formal negotiations. Liberbank declined to comment on the talks, while Unicaja said it had not hired any investment bank to look into this potential deal, adding that no due diligence was taking place. Both lenders have said in the past they are open to analysing consolidation options.