High winds have knocked back by a day Richard Parks' bid to conquer Mount Everest as part of his 737 Challenge.
The former Wales rugby union player, 33, now hopes to conquer the world's highest mountain on Wednesday, 24 May.
Parks sent an update to his back-up team that read: "Winds too high, have had to abort summit push. Extra 24 hours in death zone without planned rations.
"Going tomorrow night, got plenty of o2 and a good tent so we are all safe".
Parks and his climbing partner, double Olympic rowing gold medalist Steve Williams, had to abort their first attempt at the final climb because of the conditions, returning to camp four at the South Col.
Parks is aiming to become the first man to stand on the seven highest summits of the world and the North and South Poles.
"I was told by a climber last year that climbing in the Himalayas is about patience and perseverance," said Parks.
"And that is one of the truest things I have ever been told. The waiting, the not knowing, the uncertainty is draining.
"The effort of climbing all the way up to 7,100 metres and coming all the way back to 5,300m to then spend three or four days waiting for the window to be right for us to summit has been pretty tough."
Parks has already conquered four of the seven summits and both poles as part of his record-breaking quest.
He and Williams spent a month month acclimatising to take on Everest, and are now ready for the final push to the summit.
The pair were due to leave on Thursday from base camp to start the first part of their summit bid - the climb through the perilous Khumbu icefall and on to camp two at 6,400m.
But a change in weather meant strong winds postponed their departure.
Parks said the push for the summit will be one of the most physically and mentally demanding challenges he has had to endure during the adventure.
"I am pretty tired to be honest. Physically I feel like I am running up an escalator the wrong way at the moment, but I am also in not bad shape," he said.
"Although I am tired and worn out, I have not got the famous Khumbu cough and I haven't picked up any lurgies at base camp.
"I've got a really good appetite and physically I feel pretty good; I am as ready as I'll ever be. I'm just really looking forward to going up and getting on with it now.
"I've got a great team climbing with me. We have absolutely awesome Sherpas, probably the best Sherpas on the mountain.
"Passang, the guy I am climbing with summited this week for the seventh time; this will be his eighth summit of Everest.
"His brother Mingma is also climbing with us. Monday was his 16th summit so this will be his 17th summit, so I have a great team around me."
Parks took on the challenge after being forced to retire from rugby with a shoulder injury.
"Honestly, I would have never dreamt that I would have spent the last five months living in a tent," he added. "Life is a funny thing; when one door closes, another opens.
"You know, I learnt a valuable lesson two years ago, it was 26 May, 2009 when I was told I couldn't play rugby anymore.
"We can't control the cards we are dealt with in life, but we can control how we react to them, and I am very fortunate that over the past two years I have met individuals and companies who have been instrumental in the development of the 737 Challenge."