The 86-year-old British monarch was due to present leeks to members of the 3rd Battalion The Royal Welsh to mark St. David's Day, the BBC reported.
Instead, she will spend the weekend at Windsor Castle, where she will be "assessed in the coming days," a palace spokesman said.
It would have been her first time to present leeks, a symbol of Wales' patron saint, to the reserve force of the regiment at a parade in Swansea, CNN reported.
Byron Lewis, the Lord Lieutenant of West Glamorgan, made the presentation instead.
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