The Deputy First Minister today suggested more severe restrictions were not guaranteed, despite new figures showing 1,159 new cases of coronavirus were recorded in the past 24 hours.
Level four would see non-essential shops forced to shut, with bars, restaurants, gyms, hairdressers and visitor attractions also barred from opening – although schools would stay open.
But speaking on the BBC’s Politics Scotland programme on Sunday, Mr Swinney said this was “not inevitable”.
He said: “We are looking very carefully at all the data and having dialogue and discussions with local authorities.
“People think that maybe the battle is over because the vaccine is coming – well the battle is not over, believe you me. We’ve got a really tough period ahead of us, which is why we are looking at difficult decisions about level four.”
Mr Swinney said there was still “too much human interaction going on”.
The senior government figure explained there was “very little evidence of the virus spreading within schools”, but suggested shopping, hospitality and household visiting could be responsible for the rise in cases.
Local authorities in the Greater Glasgow and Clyde and Lanarkshire health boards were warned as recently as Friday they could be placed under the highest level of Covid restrictions.
Asked about the role of a vaccine in halting the pandemic, the Deputy First Minister said Scotland still faced a tricky period ahead.
The soaring number of cases included 459 in Greater Glasgow and Clyde and 226 in Lanarkshire.
Both areas are currently in level three of coronavirus restrictions, but Mr Swinney had previously suggested they could move up to level four – the highest tier – after a review on Tuesday.
Many local authorities in the west of Scotland have not seen a significant fall in cases. There has been a sustained increase in Renfrewshire, according to Public Health Scotland data.
The latest statistics on the virus show there are 1,241 people in hospital with Covid-19 and 100 patients in intensive care.
No new deaths were recorded in the past 24 hours and the death toll remains at 3,280, though figures from the National Records of Scotland suggest the true figure is 4,856.
Mr Swinney had previously said the Scottish Government “hoped” the restrictions in place already in Scotland “will be enough” to avoid a national lockdown, but said it must “remain one of the possibilities that exist for us”.
Speaking earlier this month, he said: "We have taken early steps to try to stem the increase of coronavirus based on the scientific advice that was given to us and have acted promptly.
"But I cannot rule out the possibility of other measures or indeed a national lockdown being required should the circumstances arise.”
His declaration comes as one of the scientists behind the first Covid-19 vaccine to clear interim clinical trials said the impact of the jab will kick in next summer and normality should return by the end of next year.
Professor Ugur Sahin, chief executive of BioNTech, said it was "absolutely essential" to have a high vaccination rate before autumn next year to ensure a return to normal life next winter.