The project is earmarked to begin next year
MPs have criticised £598m plans to modernise Birmingham's New Street Station in a report.
The plan to revamp the station in a bid to ease congestion for its 40m users a year got the go-ahead in February.
But the Commons Transport Committee said it was "not convinced" the project was "adequate" for the number of trains which could end up using the station.
It said if the station could not be adapted, the government needed to look for alternative solutions now.
This could potentially include a completely new station in the city.
But this appears unlikely as the money for the project has already been handed over by the government and the land acquisition process has started, BBC Midlands Today transport correspondent Peter Plisner said.
The New Street plan has been examined as part of the committee's report "Delivering a Sustainable Railway: A 30-year strategy for the railways?"
In it, the committee said the government must address the issue of whether the station was ever going to be able to accommodate the number of trains which may be required in two or three decades.
The plan for the station, called Birmingham Gateway, was announced by Network Rail in February 2006.
Last February, the proposal was approved and Transport Secretary Ruth Kelly said almost £400m of government money would be poured into the project.
Network Rail said the committee's report was "right to acknowledge that additional projects will be needed to grow the railway still further".
"We are in the process of reviewing the long-term needs of the West Midlands and rest of the country," it added.
The firm added that Gateway was "exactly the right project for Birmingham and the West Midlands" and was backed by the rail industry, business leaders and local people.
"The project will create a new start for the 40 million passengers who use the station each year, and greatly improve the accessibility and public perception of this vital station," it said.
The process of land acquisition began last week and more than 500 firms and residents in Birmingham city centre were told their properties could be affected by the redevelopment.