It will be Jemez's second stint with the Madrid club, which he also coached from 2012-16. He signed a contract until the end of the 2020 season. His previous clubs were Mexico's Cruz Azul and Spain's Las Palmas.
Rayo is second-to-last in the 20-team standings with 23 points, six from safety with 10 matches left. Rayo is playing in the first division for the first time since the 2015-16 season.
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