He had previously said the team would be playing at the new ground near the existing Ninian Park by Christmas 2008.
The news comes as the club faces High Court action by its financial backers Langston, which claims it is owed £31m.
But Mr Ridsdale told city councillors neither the club nor stadium was at risk from the legal action, and the club will file a defence on Tuesday.
The club has claimed it has until 2016 to pay £15m to Langston.
Mr Ridsdale told Cardiff Council's economic scrutiny committee that club officials had spent several hours with lawyers this week preparing the defence to Langston's allegations.
Responding to a question from city councillor Michael Michael, a life-long Bluebirds fan, Mr Ridsdale said he did not believe the club was at risk from the legal challenge.
Mr Michael said: "He was fairly constrained about what he could say, but he more or less said people would be silly not to get round the table and resolve it.
"What he said was that Cardiff City would be robustly defending when they go to court next week."
When it was announced in October 2006 that construction firm Laing O'Rourke had won the project contract, Mr Ridsdale said the club planned to start the 2008/09 season in Ninian Park, before moving into the new venue before Christmas 2008.
Mr Ridsdale told the meeting that the stadium was guaranteed to be built, but would not be ready until May 2009, with the pitch available from June.
He told committee members the funding for the project was in an account that was controlled by the council.
In addition to the 30,000-seater football stadium, the 60-acre Leckwith site is set to include an athletics venue, a multi-purpose sports facility and a retail development.
Mr Ridsdale told the meeting the club had fixed a "not-more-than" price of £42.3m with builders Laing O'Rourke, and expected to learn the final price next Friday.
He said the summer's bad weather had delayed the completion of the athletics track but contractors were hoping to make up time on the road and retail park.
The club has been asked to comment on Mr Ridsdale's appearance before the committee.
BBC