The Queen managed a smile as she arrived for lunch at the Jockey Club, despite having to cancel another engagement because of her strained back.
She pulled out of an afternoon at the races at Newmarket, Suffolk, but still attended the private lunch given by the stewards at the Jockey Club to mark her 80th birthday this year.
Wearing a purple coat and hat, the Queen was seen to get out of the royal car carefully, but was unassisted and smiling as she headed in to the lunch.
The 80-year-old monarch pulled out of visiting the new Arsenal football stadium on Thursday after she was advised by royal doctors to cut back on her schedule.
The Queen strained a muscle in her back while holidaying on the Balmoral estate in Scotland during the summer.
It is Newmarket's final meeting of the season on Saturday, and the racecourse had made plans to pay tribute to the Queen for her 80th birthday.
All the races have been named after notable horses owned by the monarch - Monaveen, Highclere, Dunfermline, Pall Mall, Doutelle, Aureole and Canisbay.
The Queen thoroughly enjoys racing events. She takes a keen interest in horses and always reads the Racing Post in the morning.
Buckingham Palace said she would be spending about two hours at the Jockey club lunch.
A spokeswoman said: "The Queen is going to attend lunch at the Jockey Club in Newmarket, but she's not going to the races. There will be no standing around. Doctors are taking it on a day-by-day basis."
