The Birkenhead tunnel will remain closed on Monday due to ongoing repair work.
The tunnel was due to reopen to traffic on March 1, but Merseytravel has today announced that will no longer be the case.
The travel operator said the delay was due to the work required being "considerably greater" than first thought.
It is hoped that work will be completed this week.
In an update released today Merseytravel said: "Following our planned closure of the Queensway Birkenhead Tunnel, the extent of the work required has been considerably greater than originally envisaged.
"As a result, we are sorry to inform our customers that there will now be a delay in the re-opening of Queensway (Birkenhead) Tunnel – it will not re-open as planned on Monday, March 1, 2021.
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"Our teams are working with the contractor to minimise any delay to re-opening and to ensure the work is completed fully without the need to close again in the near future.
"As soon as we understand the extent of the delay, detail will be circulated via the usual media channels."
The tunnel was scheduled to reopen on February 23, however that was pushed back with Merseytravel explaining it was taking the opportunity to complete work while traffic numbers were low during lockdown.
Maintenance, electrical, resurfacing and drainage issues were among those the repairs planned to deal with.
The operator today added: "We expect the tunnel to re-open this week and we sincerely apologise for the inconvenience and disruption caused to our customers at this time.
"In the meantime, we would like to re-assure customers that the Kingsway (Wallasey) Tunnel remains open for traffic, and bus tickets can be used to travel on Mersey Ferry and Merseyrail cross river services during the morning and afternoon peak."