Alfonso Feijoo said in April he would quit his role after Spain were thrown out of next year’s tournament in April for fielding an ineligible player during qualifying.
South African-born prop Gavin van den Berg, who has been playing in Spain since 2018, featured in two qualifiers against the Netherlands in 2020 and 2021 but was deemed not to have served the three years of residency needed to become eligible under World Rugby rules.
Spain were sanctioned five points for each infringement and fined £25,000 ($30,250).
They will be replaced by Romania at the 20-team World Cup while Portugal have taken the spot vacated by Romania in the final qualification event taking place in November.
It is the second time that Spain have missed out on World Cup qualification on these grounds.
In 2018, along with Romania and Belgium, they were sanctioned for fielding ineligible players, paving the way for Russia to qualify for the 2019 World Cup in Japan.