Mayor of London Sadiq Khan has said he cannot be sure when Crossrail will be complete.
Mr Khan said he will talk about a revised timetable at some stage, but only when he has confidence in it.
It was announced on August 31 that the capital's new east-west railway would open in autumn 2019 rather than December this year.
Mr Khan previously revealed that he only learned of Crossrail's delay two days before the announcement.
The mayor was asked on BBC Radio London if he could reassure listeners and Londoners that he has put the checks and balances in place to ensure the current situation would not be repeated.
Mr Khan told presenter Eddie Nestor: "I can't yet give Londoners the confidence that we will finish the project when we've been told by Crossrail with the most recent report.
"What we're doing now is trying to make sure we have the rigour in Crossrail Limited so we've instructed someone to do a report into governance, a very speedy report that will come back in a couple of weeks, in relation to what the governance is like now, what it needs to be, and we're doing several pieces of work.
"And at some stage I will come out and say what the revised timetable is, but only when I've got the confidence in that revised timetable."
Crossrail Ltd confirmed on August 31 that more time is needed to complete the railway's infrastructure and testing.
It was announced in July that the project's budget has been increased from £14.8 billion to £15.4 billion due to "cost pressures".
Trains were due to operate through the central tunnels from Paddington to Abbey Wood from December, when separate services on the Paddington-Heathrow and Liverpool Stree-Shenfield routes would continue.
In May 2019, direct trains from Paddington to Shenfield were due to launch, with the line fully open from Reading and Heathrow in the west to Shenfield and Abbey Wood in the east from December 2019.
Once the service begins it will be known as the Elizabeth line.