The Riverlinx consortium of Aberdeen Standard Investments, BAM PPP PGGM, Cintra, Macquarie Capital and SK E&C was named preferred bidder for the East London scheme in May.
The full contract award was due to be confirmed this summer.
But the reserve bidder STC – which contains Hochief and Dragadios – has now lodged a legal challenge.
The move means TfL has been forced to suspend the procurement process.
A TfL spokesperson said: “We are disappointed that our reserve bidder, STC, has decided to challenge the outcome of our procurement process for the design, build, finance and maintain contract for the Silvertown Tunnel.
“We are awaiting further details about the claim and will respond to them in due course.”