Medical Properties Trust, the country’s largest hospital landlord, said it would record about $350 million of write-downs related to its largest tenant, which had fallen behind on its rent, and hired a well-known restructuring adviser. 

MPT, which had long supported Dallas-based Steward Health Care System, said more write-downs are possible. The news, released Thursday after the market closed, sent shares of MPT down nearly 30% in early trading Friday. The stock is down by 70% over the past year.