HMS Queen Elizabeth is likely to head to the US coast to stand in for HMS Prince of Wales after it broke down.
The carrier had to return shortly after setting sail for training exercises from Portsmouth Naval Base on Saturday.
The warship had been on its way to the coast of North America for three months training including flight trials with F-35B Lightning stealth fighter jets.
The Royal Navy said the ship needed "complex repairs" after divers found a failed coupling on the propeller shaft.
The shaft is a combination of steel poles joined together with a shaft coupling, one of which has failed.
HMS Prince of Wales is expected to return to berth at Portsmouth Naval Base to unload crew and equipment before heading to dry dock for repairs.
Steve Henaghen, deputy naval regional commander Wales & Western England said: "Unfortunately these things happen.
"She will be going in for some repairs and that's going to be up in Scotland. It should be a relatively short period, but who knows once you open up the can and see what's what."
The planned training exercises with the US Navy, the Royal Canadian Navy and the US Marine Corps have been described by the Royal Navy as "landmark aviation trials".
It is understood that the crew of sister ship HMS Queen Elizabeth have been warned they may be sailing to the USA, altering its current plans for deployments to the Baltic and Mediterranean, although a decision has not yet been made.
Navy chiefs and the Government are believed to be assessing which of the US commitments including the Atlantic Future Forum in New York at the end of September are essential for a carrier and which can be carried out by other ships from the fleet.
The carrier had a colourful send-off on Saturday as it passed thousands of revellers during the Sugababes' set at the Victorious Festival on Southsea Common.
The warship's departure from Portsmouth had already been postponed from Friday due to a technical issue - it is not known if the incidents were related.
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