North and South Lanarkshire could be placed into the highest level of lockdown, reports say.
Level four measures cannot be ruled out by the Scottish government due to the 'level of concern' in the areas, according to a leaked letter to the council umbrella organisation Cosla.
The decision has not yet been made and it is possible the situation is 'stabilising', but the letter claims that level four restrictions are under consideration, the BBC reports.
Decisions will be made at 'the latest possible point', with the Level Four measures a potential option to stay clear of 'still greater harm, including many deaths'.
Level four restrictions would mean conditions similar to the March lockdown, and will only be rolled out if 'absolutely necessary'.
The move would bar socialising in people's homes, but a group of six people from two households would still be able to meet outside. Non-essential travel would be banned and all hospitality premises would be closed, while schools would stay open.
No other changes are under consideration for the remaining central belt areas, according to the leaked letter.
Many are currently facing harsher restrictions than the rest of Scotland, and are expected to be put into level three.
But 'encouraging signs in the data' mean five areas - Orkney, Highland, Moray, Shetland, the Western Isles - are being considered for a move down to level one, the letter says.
A Scottish government spokeswoman said of the letter: 'No decisions have been taken on what level local authorities will be in and any speculation is premature.
'Parliament will consider the framework tomorrow and decisions will only be taken once parliament has had that opportunity and on the basis of the most up to date information on prevalence of the virus.'