London Underground (LU) has said it may miss deadlines to get Tube lines upgraded.
LU managing director Mike Brown told the London Assembly transport committee it would be difficult to complete the upgrade of the Piccadilly Line by the 2014 deadline.
He also expressed doubts the Jubilee Line will be finished by October and the Northern Line by the 2012 Olympics.
He said LU's purchase of contractor Tube Lines should done on 30 June.
Tube Lines is responsible for work on the Jubilee, Northern and Piccadilly lines.
Mr Brown told the committee he had concerns about the deadlines Tube Lines has set for completing the work.
He added: "In terms if the original date for the Piccadilly Line of 2014, it will be a real stretch to get it done by that."
Mr Brown also said he will be looking at the block closure of the Northern Line for the upgrade work, which some businesses had complained about.