John Fisher, from Team Sun Hung Kai / Scallywag, was on watch when he went overboard in strong winds.
A search mission was carried out by team-mates but they were unable to find him and Richard Brisius, the President of the Volvo Ocean Race, has given a further update.
“This morning I am extremely sad to inform you that one of our sailors, John Fisher, is now presumed to have been lost at sea,” Brisius said in a statement.
“This is heart-breaking for all of us. As sailors and race organisers losing a crew member at sea is a tragedy we don’t ever want to contemplate. We are devastated and our thoughts are with John’s family, friends and teammates.
“Yesterday, just after 1300 UTC [GMT], Race Control for the Volvo Ocean Race were informed of a man overboard situation by Team Sun Hung Kai/Scallywag.
“We immediately coordinated with the team as well as the Maritime Rescue Coordination Centre, who have located a ship and diverted it towards the scene. But at current speeds it remains over a day away.
“With the rest of the Volvo Ocean Race fleet approximately 200 miles downwind, sending them back upwind to assist, against gale to storm force winds, was not a viable option.
“The Sun Hung Kai/Scallywag team conducted an exhaustive search for several hours in extremely challenging weather conditions, but they were unable to recover their teammate.
“Given the cold water temperature and the extreme sea state, along with the time that has now passed since he went overboard, we must now presume that John has been lost at sea.
“All of us here at the Volvo Ocean Race organisation send our heartfelt condolences out to John’s family, his friends and his teammates and we will do everything in our power to support them in this very difficult time.
“Team Sun Hung Kai/Scallywag has now resumed heading in a north-easterly direction.
“In fact, the team is currently in a challenging position – the weather is deteriorating and is forecast to be quite severe over the course of today.
“The crew is, of course, emotionally and physically drained after what they have just experienced. Our sole focus now is to provide all the support and assistance that we can to the team.
“We are sure that there will be many questions about how one of our sailors was lost overboard yesterday.
“We can address those after the team has been fully debriefed.
“Today, our thoughts and prayers go out to John’s family and the entire Scallywag team.”