ZURICH—Credit Suisse warned on Tuesday that it would post a fourth-quarter loss as the scandal-hit lender flagged fresh legal costs and said business in its trading and wealth management divisions had slowed. Switzerland’s second-largest lender announced plans in November to rein in its investment bankers and plough money into looking after the fortunes of the world’s rich as it tries to curb a freewheeling culture that has cost it billions. It said the investment bank would make a loss in the final quarter of the year, while the wealth management business had seen an overall drop in assets. On top of previously announced charges, Credit Suisse will make a fresh 500 million Swiss franc legal provision to settle legacy cases related to the investment bank, putting it on track for an overall quarterly loss of around 1.6 billion Swiss francs ($1.75 billion). “The cleaning up of legacy burdens from investment …