"I don't think things were going as smoothly as they could have on board and it was just something that was best for both parties really," said Walker.
Abu Dhabi, which is fifth overall in the round-the-world race, had a frustrating leg four. The Emirati team started strongly, setting the early pace in the race to Auckland alongside Team New Zealand's entry Camper and the French-flagged Groupama.
But they found themselves in a "rut" midway through the leg when the fleet split.
Three crews, including Camper, effectively cut a corner through the Solomon Islands, but Abu Dhabi were too far east to follow suit, and were soon at the back of the fleet.
Walker said that after disappointing results over the first three legs of the race, there was immense frustration on board at seeing another leg slip from their grasp.
Abu Dhabi are the most well-funded team in the race, and with a crew of highly experienced sailors were expected to be a lot more competitive than they have been.
"For one reason or another we haven't got the results that we're all here to get and that's put a lot of pressure on all of us, and everyone deals with that in their own way," the British skipper said.
"Don't forget people are tired, people are under a lot of stress. It's probably the closest thing to warfare out there in terms of what you put your body through."
It is believed Ferris will be replaced by Australian Anthony Nossiter, a veteran of two previous Volvo campaigns.
The boats set sail for the Brazilian city of Itajai on Sunday.
