Prof Mike Richards has contacted health watchdog Monitor over his concerns.
A Care Quality Commission (CQC) inspection between 30 June and 2 July found services were "only just" safe.
The Mid Staffordshire Foundation Trust has already said about 60 beds will be cut - partly due to staffing.
Prof Richards's letter, which was also sent to the Trust Development Authority and the Trust Special Administrator, said senior managers were having to spend "inordinate amounts of time" ensuring individual nursing shifts were adequately filled.
"To date, they have been able to do this. But I would emphasise the word just," he said.
The trust, which has been in administration since April 2013, is due to be dissolved in November with some services being moved to neighbouring hospitals.
Prof Richards said uncertainty over the hospital's future was "contributing to the fatigue and fragility amongst staff".
The full findings of the CQC inspection are due to be published next month,
Staffing in parts of Stafford Hospital is so threadbare that services could become unsafe if a single worker is lost, the chief inspector of hospitals has warned.