A P&O ferry that operates between Scotland and Northern Ireland must have a "small number of deficiencies" addressed before it can resume service.
The European Highlander has been inspected by the Maritime and Coastguard Agency (MCA).
It was one of two P&O Ferries vessels being checked as they try to get back to a normal schedule after sacking nearly 800 seafarers.
The Maritime and Coastguard Agency (MCA) said it began assessing European Highlander, which sails between Cairnryan and Larne on Thursday and Norbay on Wednesday.
European Highlander normally operates between Larne in Northern Ireland and Cairnryan in Scotland, while Norbay serves the Liverpool-Dublin route. The Norby was cleared to sail on Friday (22 April).
It comes as the MCA says a vessel called the Spirit of Britain, which operates between Dover and Calais, has been released from detention and can commence operations when P&O Ferries are ready.
A spokesperson for the MCA said: "The inspection of the European Highlander is now complete; there are a small number of deficiencies and the MCA requires confirmation that these have been rectified before the vessel is free to resume service.
"There are no further inspections of P&O Ferries at the moment."
The ship's detention, along with that of the Pride Of Kent vessel, caused a shortage of ferry capacity in the run-up to Easter on the key Dover-Calais route, which contributed to large queues of lorries on coastbound roads in Kent.
The firm suspended most of its sailings but reportedly only expected the disruption to last up to 10 days.