The First Minister said the rate of Covid infections in the west were stable but remained “stubbornly high”.
It means thousands of shops and other non-essential firms – such as hairdressers and all hospitality businesses – could be forced to close from Friday for an undetermined length of time.
The Scottish Government will carry out its weekly review of lockdown restrictions on Tuesday and the SNP leader will publicly confirm any changes to MSPs in the afternoon.
Glasgow Chamber of Commerce estimates that 80,000 jobs in the city alone face being put back on furlough if level four is introduced.
Speaking at her daily media briefing, Sturgeon said: “One of the issues we’re looking at very closely is whether current restrictions are reducing Covid rates quickly enough in some areas – particularly in parts of the west of Scotland.
“These areas that have stable but still stubbornly high prevalence of the virus.
“It means that we don’t have enough assurance or as much assurance as we would want to have that our hospital and intensive care services are able to cope as we go deeper into the winter.”
She added: “Moving to level four restrictions for a limited period in some areas, while not a decision we’ll ever take lightly because of the wider economic and social impacts, would help us address both of these concerns.”
It comes as a leaked briefing paper suggests ministers are preparing to place much of the central belt in tier four.
Sturgeon was earlier urged to keep gyms open if parts of Scotland go into the highest level of lockdown restrictions.
The First Minister is setting out the next review of the country’s covid alert system on Tuesday.
The highest level would close gyms, leading to fears for people’s mental and physical health being harmed.
Earlier this week, leading medical experts revealed new research on the impact of covid restrictions on self-harm and suicide.