The three-time champion jockey, 32, has not put a timescale on his return to the saddle.
"I'm not going to rush it," he said. "I want to be 100% for all the major races in the autumn."
Moore looks set to miss York's four-day Ebor Festival, one of the biggest fixtures on the flat-racing calendar, which begins on 17 August.
The major autumn races include the Prix de l'Arc de Triomphe, British Champions Day, the Breeders' Cup and the Melbourne Cup.
The lay-off will damage his chances of winning the jockeys' championship for a fourth time.
Moore, the number one rider for Irish trainer Aidan O'Brien, is second with 57 winners this year, two behind Silvestre de Sousa.
He finished as top rider at the recent Goodwood Festival with eight victories.
"I have been a bit sore for the last couple of weeks and been advised by a specialist that complete rest is the best option," he added.
"I'm going to play it by ear, but hope to be back soon."
Moore was sidelined for two months last year with a neck injury.
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The Â£42m MV Loch Seaforth made its first passenger sailing last month but is still in a "test period" and not fully in service.
Thursday's fault took five hours to fix and the ferry was cleared again for sailings.
Another ferry, the Isle of Lewis, took the passengers involved.
Bad weather has led the cancellations of Friday sailings on the Stornoway-Ullapool route and other services on Scotland's west coast.
Ferry operator Caledonian MacBrayne said withdrawing the Loch Seaforth had been an operational decision and the fault would not have prevented the ship from sailing.
A spokesman said: "Yesterday evening an issue arose with an engine room ventilation fan which required attention and an operational decision was taken to remove her from the route while it was fixed.
"While passengers were delayed, and we regret any inconvenience to them, no-one was stranded."
A spokesman added: "This was not a major issue but it required around five hours of work as the fan was in a difficult to reach location."
Leading flat jockey Ryan Moore has been advised to take "complete rest" as he recovers from a hip injury.
[NEXT_CONCEPT]
A new ferry built for the Stornoway to Ullapool route was temporarily withdrawn from passenger duties because of a faulty ventilation fan.