The GE19 bridge is being constructed by a Balfour Beatty and Carillion joint venture, as part of the £363M main works contract for the extension of the East London Line.
The bridge fell 20mm off temporary packing onto its permanent supports two weeks ago (NCE last week).
As the steel warren truss fell, one of the precast concrete slabs that forms the bridge deck became loose and dropped onto the tracks below, narrowly missing a train.
Network Rail immediately banned work on the bridge until TfL had completed an investigation and reported back on the causes of the incident. TfL must also explain to Network Rail what measures it will take to prevent a repetition.
"The investigation could take weeks if not months," said a TfL spokesman.
"We need to submit a plan to Network Rail about what went wrong and how we’re going to put it right."
However TfL remained confident that the site closure will not affect the overall programme for the East London Line.
"There will be a delay as we should be working on site and we’re not," said the TfL spokesman.
"However the whole programme is ahead so we’re not worried."
Contractors plan to use GE19 to transport rail equipment to north of the line during the projects later stages. The GE19 installation is the most complex project on the East London Line extension.