Manx Care says reopening Ramsey Cottage Hospital will take longer than expected.
The first phase of work is now expected to be completed by mid-May, allowing some services like the Minor Injuries Unit to return before TT.
A number of services had to be temporarily moved out of the hospital on Cumberland Road in December, after pest control problems.
The healthcare service had originally planned to fully re-open it this month, but says inspections found more work was needed on the building.
Health Minister Claire Christian says the work is needed to future-proof the facility.
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