Sandes has twice previously attempted to become the first South African to win the prestigious 160km trail run, finishing second in 2012 and fifth last year.
“I want to focus purely on getting in the best possible shape for the Western States,” he said in a statement on Tuesday.
Having finished second overall in the Ultra Trail World Tour last season, ending among the top five in three of the 10 legs, Sandes confirmed on Tuesday the Western States would be his only World Tour race this year.
He had initially planned to defend his title at the 125km Transgrancanaria in the Canary Islands in March, but he picked up glandular fever late last year and decided not to compete at the annual race.
“I have had to take it really easy for the past four weeks,” he said.
“It has been super frustrating and I kept thinking ‘Why me?’ But I honestly believe everything in life happens for a reason and maybe my body just needs some serious rest.”
Aside from the Western States event, Sandes confirmed he would compete in two other ultra-distance trail races this year.
“I hope to run Transvulcania (a 73km race in the Canary Islands) in May as preparation race for Western States, as well as to experience the sky running culture.
“My goal for the second half of the year is to run La Diagonale des Fous (Grand Raid of Reunion 100-miler) on Reunion Island in October.
“This race has been on my bucket list for a while and it’s also not too far from home to travel.”