The agency is set to update its figures for the 30 biggest banks across the globe within the next three weeks - and it is thought that several lenders may experience a downgrade.
For instance, Baylor Lancaster of CreditSights feels Citigroup, Morgan Stanley and Bank of America could all be under threat, while numerous banks in Europe may also face a reduction.
This round of evaluations will be the first by S&P - which has offices in 23 countries - using its new system after its previous methods were widely criticised as being too positive.
Beate Muenstermann of JP Morgan Chase & Co indicated there are likely to be some surprises on the basis that the updated system is "very complex", which has made it "very difficult to simulate results".
By Tony Aynsley