The tunnel, which links its eponymous south London neighbourhood with Limehouse, in east London, is suffering from a range of issues affecting its mechanical, electrical and communication systems.
In 2020 the total cost of repairs was estimated to be between £116m and £178m, though the cost will have risen substantially due to sharp inflation since the pandemic.
TfL said last year that refurbishment could potentially take place as early as 2025, after the new Silvertown Tunnel opens in the spring.
However it now says the tunnel’s nine-month closure will only take place from April 2026 at the earliest.
The transport body added its current work on river crossings was “absolutely essential in the short-term to keep the network operating, while also planning the work required in the future to ensure they remain open in the long term”.