canceled plans to attend the opening of a stadium on Thursday because of a strained back muscle, Buckingham Palace said.
The 80-year-old monarch had planned to attend the formal opening of Emirates Stadium, the home ground of Arsenal soccer club.
Doctors advised the queen "to reduce her workload today and will review her progress on a daily basis," a palace statement said.
The statement said the queen suffered the injury toward the end of her annual stay at Balmoral Castle in Scotland during the summer.
The queen has rarely canceled public appearances because of illness or injury, but did cancel three engagements in June 2005 because of a severe cold and sore throat.
She was also slowed in 2003 by surgery at different times on her knees.
Last week, she visited Latvia, Lithuania and Estonia in a four-day tour that required her to be on her feet for long periods, including inspecting honor guards in each nation.