The agency said the move follows a decision by Germany's Commerzbank AG to acquire a 15.3% stake in PSB, which may be increased to a majority stake in the medium term.
Agency credit analyst Eugene Tarzimanov said, "Standard & Poor's intends to resolve the CreditWatch placement in the coming months, and could raise the ratings on PSB."
This depends on whether the deal receives the approval of the German and Russian authorities, and on other developments, the agency said.
S&P said it would "assess the expected benefits for PSB attached to this transaction."
"Although it is a small acquisition from Commerzbank's perspective, it fits into its strategy to expand in Central and Eastern Europe and Russia, and stands to strengthen its position in the fast-growing Russian market," Tarzimanov said.
Moscow-based Promsvyazbank is ranked by the Central Bank among Russia's top thirty largest credit institutions, with aggregate assets of 111.1 billion rubles ($4 billion) and charter capital of 3.8 billion rubles ($139,000).
Frankfurt-based Commerzbank is the second-largest bank in Germany, with branches throughout Europe.