'Some works that are not critical to delivering the operational status of the stadium continue past this date, but still permit the FA Cup Final to be played on May 13, 2006.
The news comes just two days after shares in the Australian-based company fell as it warned that Wembley and factors related to other areas of the business were likely to knock around £70 million off 2006 profits.
Last month the group had predicted a full-year earnings figure in the region of £90 million.
Multiplex has been dogged by problems on the proposed 90,000-seat stadium, which has spurred a multi-million pound court battle between Multiplex and steel contractor Cleveland Bridge which is expected to drag on until 2007.
The statement said: 'As previously stated, such delay, if it was to occur, would be likely to lead to significant additional costs, including liquidated damages.'
The impact of the fixed-price contract was reveal in August when its construction division revealed full-year losses of £26.1 million, compared to profits of £30.8 million in 2004
The Football Association may now have to go ahead with alternative plans to switch next year's cup final.
A spokesman for the FA said: 'We are continuing to work towards playing the cup final at Wembley on May 13 but, as we have already stated, we do have the Millennium Stadium at Cardiff as a back-up.
'There is certainly no fresh concern or panic at the FA today in light of the statement issued to the Australian Stock Exchange