The Police Investigations and Review Commissioner (Pirc) said it was looking into an incident which saw police officers take several hours to follow up a report of concern about a 73-year-old in Edinburgh.
When officers arrived at the man’s home on 19 April, he required medical attention and was taken to hospital, where he remains.
This is the fourth such incident in under a year where police in the capital are being investigated over the time it took for them to respond.
All are linked to the Bilston Glen control room in Midlothian which was at the centre of controversy last year when a call about a crash on the M9 was not properly logged. John Yuill and Lamara Bell both died in the incident, which is currently being investigated by Pirc.
The couple’s car was discovered on Wednesday 8 July – three days after the crashed vehicle was reported to police by a member of the public.
Commenting on the latest incident, a Pirc spokesman said: “The Police Investigations and Review Commissioner is investigating the initial police response to an incident in Edinburgh on 19 April 2016.
“Following a report of concern about the welfare of the occupant at the property, officers arrived to find a seriously ill 73-year-old man, who remains in hospital.”
Pirc said the incident had been referred by Police Scotland’s chief constable. A report will be submitted to the deputy chief constable in due course.
The organisation is already investigating the way police dealt with the case of a man who was found dead in his Edinburgh flat last month.
The body of Andrew Bow, 36, was found by officers in East Crosscauseway.
Neighbours said they had raised concerns about his safety a week before Mr Bow was found dead.
Last year officers took 20 hours to respond to a call about 88-year-old Douglas Iggulden, who was found dead at his home in Portobello.
His wife Elizabeth was found seriously ill and died five days later in hospital.
Scottish Liberal Democrat leader Willie Rennie, who has repeatedly raised concerns about staffing levels at Bilston Glen, said: “Police officers and staff have been under extreme pressure because of the centralisation of Police Scotland.
“This is another tragic incident. It’s right that the circumstances surrounding all incidents are investigated and I’ve no doubt Pirc will get to the bottom of what’s happened.
“But there is a real case for strengthening the role of the Pirc. At the moment, there are significant shortcomings in the power to question police officers immediately after a serious incident and that needs to be addressed.”
Edinburgh South MP Ian Murray added: “I’ve had concerns about police in Edinburgh being over-stretched for some time now, since the creation of Police Scotland. I’ve raised concerns about housebreaking and community policing.”
Commenting on the latest incident, a Police Scotland spokesman said officers had responded following a “report of concern”, and the man as taken to hospital.
Chief Superintendent Kenny MacDonald added: “Whilst we cannot comment on this specific incident further, as announced at the local police and fire scrutiny board in March this year, a wider review of resources within Edinburgh has commenced.”