Ministers are being urged not to commit further public money to plans for a £315m motor racing circuit in Ebbw Vale.
Conservative AM Antoinette Sandbach said the proposals involved "huge risk" and major environmental damage.
She is leading an assembly debate on Wednesday on the plans, called a "once in a century" opportunity by fellow Tory AM William Graham last month.
The proposals will go to a public inquiry in March.
The Welsh government has given a £2m grant towards developing a scheme promising to create thousands of jobs and attract 750,000 visitors a year.
Ministers say further support depends on necessary private funding being secured.
The developers have won the right to promote the MotoGP motorbike race for five years but admit the track will not be ready to host the 2015 event.
But Ms Sandbach, a north Wales AM who speaks for her party on the environment, said the project will also miss the deadline for the 2016 race.
A Circuit of Wales spokesman said: "The completion date for the track is dependent on many variables, including the conclusion of the public enquiry, the weather and completing the due diligence for the environmental and planning processes.
"Following a positive outcome from the public enquiry, we plan to commence work on-site in 2015 and to host the British leg of the MotoGP championship in Wales as soon as phase one of the development is completed."