The 44-year-old man had been walking in San Francisco with his 23-year-old niece on Friday when he was attacked by a man and a woman.
The tourist reportedly struggled to hold on to the bag holding his passport, money and a mobile phone leading to a scuffle.
The man, who has not been named, was taken to San Francisco General Hospital. His niece was not injured, Sky News said.
A spokesman for the Foreign Office said: "We are in contact with the family of a British national who is in hospital in San Francisco, and will continue to offer support at this difficult time."
Police spokesman Carlos Manfredi said tourists were not likely to have been specifically targeted. “It happens to everybody, so every now and then there’s going to be a tourist in the mix," he added.
British tourist left with 'life-threatening injuries' after San Fran mugging
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