BSI is set to change ownership as the auction to acquire the brand from BTG is expected to conclude in February.
EFG International, led by Greek billionaire Spiros Latsis, is currently the leading contender with a bid of 1.3 billion francs.
The auction has narrowed down to a competition between EFG International and a consortium formed by Italian Bi-Invest and BancaStato, which has the support of UBS.
The future of BSI and its potential new ownership will be determined in the coming weeks following the brief tenure of BTG Pactual.