The latest report on the London Underground's public-private partnership has raised fresh questions about the ability of key contractors to deliver on their plans.
An annual review, produced by Transport for London (TfL), suggested Tube Lines may struggle to complete a key area of its work for this year.
Tube Lines has a 30-year contract for the maintenance and upgrade of infrastructure on the Jubilee, Northern and Piccadilly lines.
Metronet, which was involved in the upgrade of other lines, went into administration in July 2007 at a cost taxpayers of up to £410m.
TfL said it now has "grave doubts" over Tube Lines and Bechtel's ability to deliver an upgrade of the Jubilee line by the end of December.
The London transport body said it had already agreed to extra weekend closures of the line to deal with the delays.
Mayor of London Boris Johnson called on Tube Lines to "get its act together" on the Jubilee line.
"I am hugely frustrated at their progress to date, which is simply unacceptable," he added.
"Tube Lines' hunger for more Jubilee line closures has stretched the patience of Londoners and business almost to breaking point.
"Before we can consider any more disruption, we must have confidence they will deliver."
Meanwhile, London Underground (LU) managing director Richard Parry said the transfer of Metronet to TfL had meant changes to "the fabric of the PPP itself".
"The legacy of inheriting programmes that were overspent and behind schedule has hit us hard," he said.
Parry added that working relationships with Bombardier and Westinghouse had improved since the "dysfunctional PPP arrangements" were abandoned.
Commenting on the report, chief executive of London First Baroness Valentine said that while upgrade work had led to improvements, "it's clear that there are lessons to be learned by all sides in the way it has been managed".
"The extended closures on the Jubilee line are highly disruptive for business, while LU's repeated claims that Metronet is a transformed creature since being taken in-house seem a little hollow without external verification," she added.
"The most important thing for passengers and London as a whole is that these hitches lead to improvements and that we get on with the next phase of transforming the Tube."
