In a Covid-19 update to MSPs on Tuesday, Mr Yousaf said the decline in case numbers had recently slowed and there were “early signs” of another increase.
Meanwhile the NHS in under more pressure than ever before, with hospitals across the country “at, or close to capacity”, he said.
Cases remain "much lower” than the previous peak around the start of September, Mr Yousaf said.
But he added: “The decline in new cases has halted in recent weeks and, at around 2,500 new cases per day, it is still at a level well above previous lows.
"There are early signs that case numbers may increase again hereafter and so the situation remains precarious.”
Mr Yousaf added: “The Scottish Government continues to explore all options for how to respond to the evolving pandemic.
"We will not hesitate to strengthen the protective measures in place if it proves necessary to do so.”
Mr Yousaf’s comments came as Scotland recorded 26 coronavirus-linked deaths and 2,010 new Covid-19 cases in the past 24 hours.
The daily test positivity rate was 13.5 per cent, up from 10.8 per cent the previous day.
There were 932 people in hospital on Monday with recently confirmed Covid-19, up one on the previous day, with 63 in intensive care, down five.
Mr Yousaf cited bonfire night celebrations this week as being one possible reason for a rise in cases, as well as the protests and demonstrations that will take place during COP26, with tens of thousands of people expected to march through Glasgow at the weekend.
The health secretary said that while Scotland had a “strong tradition of peaceful protest”, people should “think very carefully about their behaviours and their impact on services – as well as the risk of spreading the virus to others”.
He continued: “Moreover, we know that, with people meeting indoors more often as it gets colder, there are more opportunities for Covid to circulate.
“And we are also approaching the winter flu season, which could put further pressure on the NHS.”
Mr Yousaf also underlined the current strain on the NHS.
He said: “The entire health and care system is currently under considerable pressure.
“Right across the country, hospitals are at, or close to, capacity.
“The social care system is also under enormous pressure and reporting an increase in the number of people requiring care packages.
“We see a continued high number of cases, which means that the NHS remains under more pressure than at any time during its 73-year history.”
The health secretary reiterated an earlier announcement of £10 million of funding aimed at “deploying physiotherapists and occupational therapists at A&E units to help triage and treat patients who would otherwise wait to see nursing staff”.
He said: “The new funding will provide more specialists such as social care workers and Allied Health Professionals on hospital rotas, and extended opening hours for pharmacy and diagnostic services such as scanning and ultrasound to speed up referrals.
“It will also support extra staff for peak public holidays.”