The city council has revealed a list of 93 separate areas of land around the shopping mall that may have to be compulsorarily purchased.
Some of the areas needed for the massive development at the top of Buchanan Street are only 5sq ft while others cover thousands of square feet.
The detailed list of compulsory purchase orders will now be sent to Scottish Ministers for their approval.
The council notice says it is necessary to acquire the land to achieve the development and redevelopment of - and substantial improvements to - the Buchanan Quarter area.
Work will include the extension and refurbishment of Buchanan Galleries and public realm improvements.
The extended Galleries will deliver 1.2m sq ft of shopping, leisure and restaurant space and will be anchored by two major flagship stores.
They are a new 150,000sq ft Marks & Spencer and a reconfigured 300,000sq ft John Lewis department store.
It is hoped initial work on the development will start in October this year with the main works getting under way in January next year and finishing around Easter 2018.
The huge extension is being carried out by developer Land Security.
Development director Nick Davis said: "This is an important milestone in progressing this exciting development in Glasgow City Centre.
"Compulsory purchase orders are not uncommon in developments of this scale and this process will pave the way for our £300 million investment in the city's Buchanan Quarter.
"The new retail, leisure and transport hub will create over 2000 jobs and provide a significant boost to the local and national economy."
Land Securities was also behind the new shopping complex opposite Buchanan Galleries, which includes Paperchase and Forever 21.
A council spokesman said: "The CPO is essential in order to enable the development of which the council is supportive.
"The CPO focuses purely on commercial properties and is at no cost to the taxpayer."
City council leader Gordon Matheson, who represents the city centre, said: "This next step in developing the Buchanan Quarter will not only improve the city centre's public realm and infrastructure, but also deliver more than £300 million of private sector investment to the heart of Glasgow and new jobs to Glaswegians.
"The enduring interest from retailers underlines the faith investors are showing in Glasgow and further underlines Glasgow's popularity with shoppers and visitors."
Bosses at the shopping mall have already pre-let more than 20 per cent of the units.
And it is hoped almost half of the 100 new stores will have been leased by October.
Earlier this year, the Evening Times revealed luxury chain Showcase Cinema de Lux had signed up to run a ten-screen cinema in the new extension.
A report that went before city councillors said: "Buchanan Partnership has exceeded the 20 per cent pre-let target with strong interest from new-to-Glasgow brands."
The company is a joint venture between Land Securities and Henderson Global Investors.
Mr Davis said: "Glasgow is the biggest retail destination in the UK outside London and the interest that has been shown in the Buchanan Quarter and the extension to the Galleries highlights the continuing desire by retailers to come to the city."
He claimed the success of the new shopping complex opposite Buchanan Galleries in Buchanan Street is an indication of the demand to open up shops in the city.
Mr Davis added: "It is not showing any signs of letting up."
Stuart Patrick, chief executive of Glasgow Chamber of Commerce, said: "The pre-let achievement of Buchanan Galleries' extension reflects on the overall strength of Glasgow's city centre."
Mr Patrick agreed the development will create nearly 2000 jobs.
Liz Cameron, the council's executive member for jobs and the economy, said: "The interest from retailers underlines the faith investors are showing in Glasgow."