Fitch Ratings downgraded Credit Suisse Group's long-term default rating by a notch to A-minus and its viability rating to a-minus from a, citing the Swiss bank's reliance on difficult capital markets.
The agency also blamed the economic slowdown in the Asia-Pacific region which would put pressure on the lender's new business model.
"We expect execution of strategic restructuring to remain more challenged by prevailing unfavorable fixed income and equities capital markets than was the case when it was announced in October last year, particularly in Europe and Asia," it said.
Earlier this month Switzerland's second-biggest bank posted a second straight quarterly loss, in its worst start to a year since the financial crisis.
The bank's mark-to-market losses in these two quarters were related mainly to securitised products, distressed credit and certain underwriting positions, Fitch said.
But the planned exit from distressed credit and European securitised trading, and sharp reduction in these exposures, would help earnings, it added.
Even so, the current year's performance would be weighed down by subdued client activity in debt and equity capital markets, larger-than-expected restructuring costs and an initially significant drag from activities earmarked for wind-down and booked in the strategic resolution unit.
While the expected settlement of U.S. mortgage matters during 2016 should remove much of the uncertainty, Fitch said it expects conduct and litigation risk would remain material contingent liabilities for the foreseeable future.
Fitch also downgraded the long-term default rating of subsidiaries Credit Suisse International and Credit Suisse (USA) Inc. to A-minus from A.