Michael Cunnah, the chief executive of Wembley National Stadium Ltd, invoked the construction industry's version of "leaves on the line" as he warned that, although the target date for completion was 31 March, a hard frost of the kind that has been forecast this winter could put the finish back.
Severe wintry conditions would add a further burden to the builders, the Australian firm Multiplex, who have already admitted they are losing money on the £757m project.
"If there is this deep freeze people are talking about then Multiplex are going to have a hard time digging the pitch and then putting the foundations in," Cunnah said yesterday. "Things like that could possibly put you off track.
"Therefore we've all got to be prudent. We're going 100 per cent to make sure the Cup final happens here next year, but absolutely nobody, not even Multiplex, can give us guarantees.
"It'll be finished when it's finished," he said. "31 March is the day Multiplex are working to but we have to see how fast they go and what progress they make in the next few months.
"We'll take it as soon as it's ready because the busiest time for Wembley is the summer because we have got cup finals, England internationals and very exciting rock concerts.
"Personally I'm hoping that it certainly will be 31 March and if it [is not, then] it will be very soon thereafter."
The Football Association has already booked the Millennium Stadium in Cardiff should Wembley not be ready for the final on 13 May. Brian Barwick, the FA chief executive, has also expressed doubt that the stadium will be finished.
"If Multiplex is true to its word we have every chance of staging the Cup final at Wembley," he said. "Equally, we have taken the prudent step to book Cardiff's Millennium Stadium."
Richard Caborn, the Sports Minister, spoke earlier this month about his hope that Multiplex - which has announced that cost overruns on the project will probably rise to £75m following a dispute with its steel supplier - would meet the 31 March deadline.
"They say the Cup final will be there, barring six feet of snow or something like that," said Caborn, who had spoken to the company's ex-chairman and managing director.
"They have given me reassurances that it will be ready for the Cup final," Caborn added. "I do believe them. From what I have seen, it will be on time - it won't be on price - but it will be on time."
Following Cunnah's comments, the bookmakers Coral have been forced to alter the odds on next year's FA Cup Final not being held at the new Wembley Stadium from 6-4 to 6-5.Reuse content