St Mary's Medical Centre in Nottingham closed by CQC
More than 1,000 patients were left without a doctor when a GP surgery was suddenly shut by a health watchdog.
The Care Quality Commission closed St Mary's Medical Centre, in Nottingham, until further notice over "a number of concerns" but refused to be specific.
A previous inspection of the clinic found it required improvement. The surgery was unavailable for comment.
The 1,100 registered patients now need to go to Rise Park Surgery or Hucknall Road Medical Centre.
Ward councillor Alan Clark said: "It's a great concern that this has happened. I'm supportive of the idea that medical practices are inspected - there's clearly something of grave concern there."
Mr Clark said that patients with a repeat prescription or an appointment this week would be contacted by the NHS and everyone else had been sent a letter.
The CQC said it would reveal why the Top Valley surgery had been closed when the doctors had had time to respond.