Opposition MSPs hit out at Mr Yousaf, who made the comments on BBC’s Good Morning Scotland on Wednesday as he suggested the NHS was facing an “extraordinarily difficult winter”.
While he pledged any additional cash that could be found would be spent trying to ease the pressure on the health service, the health secretary said people should consider whether it was “absolutely critical” for them to call for an ambulance.
The recent surge in coronavirus cases has resulted in rising numbers of patients in hospital with the virus, with the total now more than 1,000 again.
This in turn is putting pressure on other parts of the health service.
It emerged last week the average wait for an ambulance had reached six hours, while the number of patients who spend more than the target time four hours in accident and emergency has hit record highs.
Conservative public health spokesman Dr Sandesh Gulhane said: “It is astonishing to hear the SNP’s health secretary try to discourage people from calling for an ambulance.
“This sort of reckless messaging could put lives at risk.
"When people suffer conditions like heart attacks or strokes, they might think twice about calling an ambulance, which could lead to unnecessary deaths.”
Scottish Liberal Democrat leader Alex Cole-Hamilton said: “Humza Yousaf is proving a reckless health secretary. Encouraging people not to seek treatment is a huge gamble.”
And Labour health spokeswoman Jackie Baillie also criticised Mr Yousaf, saying: “Ambulance services are in crisis due to the SNP’s failure to support frontline workers and paramedics."
Mr Yousaf had earlier told BBC Radio Scotland: “We are in for an extraordinarily difficult winter.
“Looking at the data the last time we had 1,000 patients in hospital with Covid was December 2020. Our A&E presentations now, when we have the same number of Covid patients, is 40 per cent higher.”
The health secretary added: “I can’t get away from the fact that we are in an extremely challenging winter and that is why we’re investing as much as we possibly can.”
And he pledged: “Whatever money I can find, additional resources I can find to help the NHS, I can promise you that will all be spent to tackle what will be a challenging autumn and winter.”
The Scottish Government has already outlined a £1 billion NHS recovery plan and Mr Yousaf also stressed the ambulance service was being given an “extra £20 million injection” to help boost staff numbers.
“We are beginning to see more and more ambulance staff recruited,” he said.
“That recruitment is happening now, so we are helping to staff up the ambulance service.”
When asked directly if people should “think twice” before calling for ambulance, Mr Yousaf said: “Yes is the short answer to that.”
The health secretary added: “I don’t doubt that people do that because they are in distressing situations, I think most people only call when they are in that extreme distress.”
Mr Yousaf said people who were “picking up the phone to call 999 to call an ambulance” should consider if this is “absolutely critical” – although he stressed if it was they should “of course make that call and the ambulance service will get to you as quickly as they possibly can”.
Call handlers for the Scottish Ambulance Service are understood to be dealing with about 10,000 more 999 calls a month than last summer.
Commenting separately on the roll-out of vaccinations to 12 to 15-year-olds from Monday, Mr Yousaf said children who chose not to have the jab should not be stigmatised.
But he stressed the expansion of the programme would help address the mental health impact on children from missing school.
Mr Yousaf said: "As the health secretary I will be encouraging as many young people, and as many people in general, to get vaccinated because I believe in the protection of the vaccine.
"But we are going to have to work really, really hard to say that there is no stigma here. It is people's choice."
The health secretary’s reassurances came as the number of confirmed or suspected coronavirus deaths rose by 18 to 76 in the past week.
Data from National Records of Scotland (NRS) shows that as of September 12, there have been 10,688 deaths registered in Scotland where Covid-19 was mentioned on the death certificate.
The latest Scottish Government figures published on Wednesday meanwhile showed Scotland had recorded 30 coronavirus-linked deaths in the previous 24 hours.
Twelve of those who died in the week of September 6-12 were under 65, while 13 were aged 65-74 and 51 were over 75, according to NRS data.
Glasgow City Council and North Lanarkshire had eight deaths each in that period, with seven deaths in South Lanarkshire, six deaths in Dundee City, and five deaths in the City of Edinburgh.
Sixty-two people died in hospital, six in a care home and eight at home or in a place that was not an institution.
The statistics are published weekly and cover all deaths registered in Scotland where Covid-19 was mentioned on the death certificate.
They differ from the lab-confirmed coronavirus deaths announced daily by the Scottish Government because the NRS figures include suspected or probable cases of Covid-19.
Pete Whitehouse, NRS director of statistical services, said:“Between March 2020 and August 2021, 93 per cent of people who died with Covid had at least one pre-existing condition, the most common condition being dementia or Alzheimer’s disease.”
The figures showed that of the 10,609 deaths involving Covid-19 between March 2020 and August 2021, more than nine out of 10 (93 per cent) had at least one pre-existing condition.
However, younger people dying with Covid-19 between March 2020 and August 2021 were more likely to have no pre-existing conditions.