The builders constructing Melbourne's West Gate Tunnel predict it is unlikely to be finished by its deadline, as a soil contamination issue persists.
But toll company Transurban, which is leading the project, is optimistic it can find a way to deliver the tunnel on schedule by 2022.
The state government also expects that will be the case.
Transurban has committed to building the alternative route for the city's heavily congested West Gate Bridge with joint-venture builders CPB Contractors and John Holland.
But in its half-year results released on Tuesday, Transurban, which approached Labor to build the tunnel before the party was elected to government in 2014, noted the "project schedule is under review".
The toll giant's chief executive Scott Charlton says the builders have flagged a 2022 finish is unlikely, but his organisation is optimistic the deadline can be met.
"The contractors in CPB and John Holland have informed us that the project ... is unlikely to be completed by the end of 2022, and there is significant pressure on the project schedule," he said on Tuesday.
"However, notwithstanding what the JV (joint venture) partners said, and the challenges, we're working closely with our project partners to implement some opportunities that would enable us to deliver the project in 2022.
"We believe it is possible to deliver the job by 2022, but the schedule is under pressure."
The builders have tried to terminate their subcontract with Transurban over contaminated soil at the site, including its disposal, but Transurban says it does not consider the contract termination to be valid.
It is working with the builders and the Andrews government to resolve the issue.
"We're making good progress on a technical solution and hopefully we'll have something in the next few months," he said.
The state government has maintained confidence Transurban and the builders can resolve their differences and finish the job in time.
"Is it tight? Yes, it is. Is it difficult? Yes, it is. Do we have some issues to resolve? Yes, we do," Acting Premier James Merlino told reporters on Tuesday.
"But the CEO of Transurban made it clear they'd continue to work towards a 2022 completion date.
"We have a contract in place, we expect it to be honoured."