Sherlock co-creator and writer Steven Moffat says he is "annoyed" a US network is working on an American version of the hit UK show.
CBS announced earlier this year they would be filming a pilot called Elementary.
The US programme will feature Sherlock in New York and Watson will be played by 43-year-old Lucy Liu.
Steven Moffat says he hopes it will be good or it may degrade the Sherlock brand.
"It isn't a version of our show," he said. "They've just decided to go off and do one of their own, having been turned down by us to do an adaptation of our version.
"So how do you think I feel about it? Annoyed is in there."
The US Sherlock will be played by British actor Jonny Lee Miller.
If the pilot is successful, it will be turned into a TV series which will air on US television in the autumn.
"The bigger problem for us with Elementary is, what if it's terrible? What if it's awful? Then it degrades the brand," he said.
"I remember there was a legitimate American version made of Coupling, actually adapted from our version.
"It was terrible and it was a disaster and it did sort of diminish the original.
"So if there's this completely unrelated rogue version of Sherlock going around and it's bad, it can be bad for us."
So far CBS hasn't revealed which Arthur Conan Doyle stories will be made.
Talking at the Royal Television Society Awards, Moffat dismissed the idea that legal action had been taken over copyright.
"We don't own Sherlock Holmes," he said. "We don't even own the idea of updating it. It's been done before.
"I hope they know their Sherlock Holmes very, very well indeed because we know what's in our show and wasn't in the original.
"So if we did discover our material had made it into somebody else's show we would have a problem with that. If there is no such incidence of that, then there's nothing we can object to."
When asked about a possible fourth series, Moffat revealed that Sherlock star Benedict Cumberbatch was keen to continue playing the lead role.
Bolded the important parts. This pretty much sums up how I feel about Elementary.
Source: 1 + 2