Three floors at a stalled new hospital must be rebuilt because of "complex" structural flaws left by construction giant Carillion, a review has found.
Building work at the already delayed new Royal Liverpool Hospital was halted in February last year after Carillion's collapse.
The review by structural engineers from Arup found three of 11 floors require strengthening.
The hospital was originally due to open in March 2017.
Dr Peter Williams, chief executive of the Royal Liverpool and Broadgreen University Hospitals NHS Trust, said a new completion date had not been set to avoid "raising expectations".
The work will involve "stripping back" areas that were near to completion, the trust said.
The Department of Health has been contacted for a response on behalf of Carillion.
The project, a 646-bed hospital originally expected to cost £335m, has been repeatedly delayed after asbestos was found on site and remedial building work was also needed.
Structural work, which will begin later this month, includes strengthening existing beams, reducing loads and putting in additional support for torsions, Jim Bell, director of structural engineers for Arup, said.
Mr Bell said it was "highly complex" and required more than 220 cubic metres of new concrete and 165 tonnes of new fabricated steelwork.
New contractors Laing O'Rourke, who also built Liverpool One and Alder Hey Children's Hospital, said they were working to finish the building "to the high standards required".
Control measures are already in place so that there are no immediate risks to workers in the building, project director Andy Thomson added.
Some of the cladding of the new hospital will be removed for access.
Dr Williams said: "Once the programme [to complete the new Royal] is finalised and the costs are all accounted for we'll confirm timescales and costs.
"We owe it to everyone to not raise expectations with speculation, until everything is signed, sealed and delivered.
"Our priority is to deliver the state of the art facilities that our patients need and the world class hospital we've all been waiting for."
Liverpool Mayor Joe Anderson said it was a "shambles", adding: "In 2010 the government reduced and took away the right of local authorities to inspect buildings in the private sector.
"That is why I'm calling for an inquiry into why this was allowed to happen."
Dame Louise Ellman, MP for Liverpool Riverside, said: "Carillion's calamitous collapse left Liverpool in the lurch."
"It is deeply disappointing that the discovery of significant construction defects will result in further delay," she added.
"The new Royal should have opened two years ago.
"It is vital for the necessary work to be completed as a matter of urgency, so that the people of Liverpool can have this much-needed new facility."