The East Lancashire Hospitals NHS Trust has won planning permission from Burnley Council for the gravel-surfaced car park on the St Andrews Recreation Ground (also known as Rakehead Rec).
They say it is needed while a new multi-storey car park is built for use by patients, visitors and staff.
Residents in nearby Hind Street submitted five letters of objection to the scheme.
They said the Rakehead Rec is an important part of the fabric of the local community which may be lost by further creep by the hospital into open space.
The planning permission has five conditions including that the use should stop no later than the July 1, 2024.
In a report, planning officer Janet Filbin told councillors: “It is accepted that a short term need for the parking of hospital staff is a concern for the delivery of hospital services.”