The Queen cancelled a trip to Arsenal's new multi-million pound stadium after suffering a back injury.
The Duke of Edinburgh attended the opening instead
Buckingham Palace said she could not visit the north London Emirates ground because she has strained a muscle.
The 80-year-old monarch had been due to meet Arsenal staff, fans and players, including manager Arsene Wenger and captain Thierry Henry.
The Duke of Edinburgh attended the ground's official opening while the Queen met visitors at the palace.
Speaking at Arsenal's new ground, Prince Philip said: "The Queen asked me to tell you all how very disappointed she was not to come here today."
Arsenal manager Arsene Wenger, meanwhile, joked: "We are very honoured and proud that the Queen wanted to attend and that the prince replaced her but in sport an injury can happen at any time."
The royal couple completed their first ever tour of the Baltic states Lithuania, Latvia and Estonia last week, after spending time at Balmoral.
And Thursday's cancellation came on the advice of doctors, although the Queen intends to continue keeping some engagements at the palace.
A spokeswoman for Buckingham Palace said earlier: "Her Majesty the Queen has reluctantly agreed to cancel a visit to Arsenal football stadium today due to a strained muscle in her back.
"Doctors advised Her Majesty to reduce her workload today and will review her progress on a daily basis.
"The strained muscle was sustained at the end of the Balmoral period and has not improved during a busy two weeks of engagements."
While the Duke of Edinburgh continued with the stadium visit, the Queen was due to meet the ambassadors of Namibia and Belgium at Buckingham Palace.
Buckingham Palace said a decision would be made on Friday about whether the Queen was fit to attend the races at Newmarket, as well as attending a lunch with the stewards at the Jockey Club.
The Queen rarely cancels appointments.
But in June last year, she had to cancel three engagements after catching a bad cold and suffering from a sore throat.
And in 2003, she had keyhole surgery on both her knees.
The Queen used a walking stick while she was recovering and her official engagements were scaled down.