Tens of thousands of rail commuters who rely on Southern will be unable to reach London Victoria until 10 January.
The station is the terminus for trains to south London, Surrey and Sussex, as well as the Gatwick Express airport service.
Lines are currently closed due to planned Network Rail engineering work, with reduced services routed to the alternative hub, London Bridge.
Trains were due to resume on 4 January. But Southern is now telling passengers: “There will be no Southern or Gatwick Express services at London Victoria, Battersea Park, Clapham Junction or Wandsworth Common until Monday 10 January.
“The times of trains on all routes will be changed and, on many routes, services will be reduced.”
Some trains from the south coast will be re-routed to London Bridge. But suburban services will terminate at Balham, where passengers must transfer to the London Underground.
Links from Clapham Junction to Milton Keynes, from East Croydon to London Bridge via Forest Hill and from Epsom to London Bridge via Carshalton Beeches will not run.
The Gatwick Express, which resumed only three weeks ago after an 18-month closure, has been suspended again.
Southern blames “the significant ongoing impact of Coronavirus, particularly in terms of staff sickness which businesses and transport operators across the country continue to see”.
For several years commuters on Southern experienced repeated disruption due to strikes over the role of guards.
Other rail operators are introducing emergency timetables to contend with the number of staff who are off work.