It was announced last month that Johnston had conditionally acquired the papers for £11.2m.
The OFT is now considering whether the sale would create a relevant merger situation under the merger provisions of the Enterprise Act 2002.
If so, it will then consider whether the sale would be expected to result in a substantial lessening of competition.
Written representations need to be submitted to the OFT by February 20.
The sale also includes the Ayrshire Extra, Lanarkshire Extra, Paisley and Renfrewshire Extra, Glasgow Southside and Eastwood Extra, and Bearsden, Milngavie and Glasgow Extra.