A hi-tech unmanned submarine will be used to scour the seabed off the Channel Islands for wreckage of the plane that was carrying the footballer Emiliano Sala as part of a family-led operation funded by fellow players and well-wishers.

The expert leading the search said they would use the remotely operated vehicle (ROV) to comb an area of around 25 square nautical miles and they believed there was a good chance of finding the plane, which vanished on Monday last week en route from Nantes in France to Cardiff.

Facebook Twitter Pinterest The shrine to Emiliano Sala at the FC Nantes training

ground. Photograph: Eddy Lemaistre/EPA

David Mearns, a specialist in finding shipwrecks, said that if the plane’s wreckage was located, the next step would be to try to recover it. He said Sala’s family was determined to establish what happened to the Argentinian footballer.

Details of the private search were revealed as the Cardiff City manager, Neil Warnock, said he has questioned his own future at the club following the disappearance of the plane.

Emiliano Sala’s disappearance has made me consider retiring, says Neil Warnock Read more

“You think 24 hours a day about whether to carry on,” Warnock said. “It’s impossible to sleep. I’ve been in football management for 40 years and it’s been by far the most difficult week in my career, by an absolute mile.”

Facebook Twitter Pinterest Cardiff City’s manager, Neil Warnock. Photograph: Athena Pictures/Getty Images

Warnock said he believed he had been a passenger of the pilot who was lost along with Sala, Dave Ibbotson, from Lincolnshire. He said: “I’d been to Nantes a couple of times and I do think I had that pilot, who I thought was a fabulous pilot. So I just can’t comprehend it.”

The manager revealed that he had invited Sala to watch Cardiff’s Premier League game at Newcastle on Saturday 19 January, but Sala chose to return to France to gather his belongings and say farewell to his Nantes team-mates before his first training session at Cardiff last Tuesday.

“From my point of view, I have thought many a time: ‘Should I have insisted he came up to Newcastle?”’ Warnock said. The manager had said Sala told him: “‘I’ll score you the goals” and the manager had replied: “I know you will.”

The official search, which was led by the Guernsey harbourmaster, Capt David Barker, was terminated last Thursday.

Pleas for the official search to resume have come from the 28-year-old player’s family, the Argentinian footballers Lionel Messi, Diego Maradona and Sergio Agüero, and the country’s president, Mauricio Macri.

Donations from footballers including Manchester City’s İlkay Gündoğan helped a GoFundMe page raising money for a private search to pass the €300,000 (£260,000) target.

On Monday, a week after Sala and Ibbotson vanished, members of Sala’s family chartered a plane and re-traced the flight path of the lost aircraft to try to help them build a picture of what happened.

Two fishing boats continued to search the area just north of Guernsey where contact with the plane was lost.

Speaking at Guernsey airport with members of Sala’s family beside him, Mearns said a search vessel was being mobilised and was expected to be in the area by the end of the week, although poor weather conditions mean it may be delayed until the weekend.

“We are getting ready for the next phase, which will be the underwater search,” said Mearns of Blue Water Recoveries. He said the last known position was north of Hurd’s Deep, an underwater valley used as a dumping ground for radioactive waste.

The area that Mearns will be focusing on is 65m deep and is regularly fished by scallop dredgers, making the hard seabed smooth. Mearns said the currents were strong and there were other wrecks there, which made it more tricky, but he said the sea bottom was easily reachable with the ROV.

He said: “We cannot guarantee we will find the plane, but we think we have a very good chance … The family is determined to get answers they don’t have now - the only way is to find this missing plane.”