Problems began on the line at the end of November, when around half the Piccadilly Line fleet was taken out of service for repairs, due to damage caused by larger-than-usual quantities of wet leaves on the tracks.
A TfL spokesman told City A.M. that, due to an unprecedented level of repairs necessary, there are currently 54 trains running on the line - with 79 trains needed for full service at peak times
Around two trains are being put back into operation per day, which theoretically means that the line should be back in full service within two weeks - however, it's possibly that more trains will need to be fixed, which means the disrupted service is likely to last until 2017.
Piccadilly Line drivers and the RMT union have said the issues with the trains are due in large part to wheels that were fitted just one year ago.
A spokesman for RMT said the union has called for an investigation into a refurbishment of the trains that took place last year, part of which involved fitting them with new wheels which have now had to be repaired because they lock when they come into contact with wet leaves.
The RMT has called for a complete closure of the Piccadilly Line until all the trains are fixed, and also wants the 16 December start date for Night Tube services to be postponed - a demand that TfL has rebuffed.
Meanwhile, drivers on the Piccadilly Line will walk out tomorrow evening for a 24-hour strike. They will be joined by drivers on the Circle and Hammersmith & City Lines. The industrial action will begin at 9.30pm and run until the same time on Wednesday 7 December.