In January, Transport Secretary Patrick McLoughlin unveiled a paper saying the Government's preferred line for the new service will stop south of the border.
But a city council expert has warned that could result in Scotland's largest city being disadvantaged.
Transport policy and planning manager Tony Hughes said: "Whereas it now takes twice as long to reach Glasgow from London by rail as it does to reach Manchester, in 2033 it will take almost four times as long.
"And while continental-gauge high speed rail trains will be able to travel directly from Europe to Birmingham, Manchester and Leeds, passengers from Scotland will need to travel to London or one of these cities to join them."
Glasgow has consistently argued that high speed tracks should reach Glasgow and Edinburgh at the same time as they reach Manchester and Leeds.
Mr Hughes said: "Only the construction of dedicated high speed rail lines over the full length of the route between Glasgow and London will deliver the journey times of around 2hrs 30mins necessary to make Glasgow an attractive location for inward investors."
And Mr Hughes warned the wording of the recent Government paper gives "no certainty" that Glasgow will ever be connected to the UK high speed network by dedicated tracks.