Indulging the monsieur in the hope this helps others rather than just him...
City - the massage place in the hairdressers next to Monument seems to have closed, which is a pity as I was looking forward to erecting my own monument there. Other than that, in the square mile proper there's nothing as premises have to be licensed by the local authority (there is the indie Thai outfit on Gumtree near Bank though) and the City council clearly don't allow it. The moneybag spoilsports.
Adjacently - as pointed out, there's three sets of premises just over the border in Tower Hamlets around Middlesex Street, plus the two Chinese joints near Liverpool Street (Five Elements and the other one at the junction of Middlesex/Bishopsgate).
There's also Leather Lane and the Holborn one if you fancy stretching your legs. (is Exmouth Market one still there?)