Real Madrid's Castilla youth team have missed out on a place in the promotion playoffs after they were beaten 2-0 at Navalcarnero on Sunday.
Santi Solari's team took just one point from their last five games to fall to ninth in the Segunda B table, meaning they will remain in the third tier for a fourth consecutive year.
The poor recent run had all but dashed their promotion hopes, and former Madrid and Argentina midfielder Solari benched regular starters including Enzo Zidane and Aleix Febas against 15th-placed Navalcarnero.
He saw his side slip to another defeat after centre-half Javi Sanchez was sent off early in the second half.
"Real Madrid Castilla were not able to get a positive result from their trip to Navalcarnero," a club statement said.
"The game, evenly matched on the whole, was changed by a penalty in the 51st minute. From the home side's set piece the ball struck the hand of Javi Sanchez, with the referee pointing to the spot and sending off the Real Madrid centre-back.
"With this defeat, it is now mathematically impossible for the reserves to make the promotion playoffs."
Senior coach Zinedine Zidane was in charge of Castilla from summer 2014 until January 2016, guiding the team to sixth in his first full season in charge.
After he replaced Rafa Benitez as first-team coach, results improved under Ivan Ramis in the final months of 2015-16 but the team lost out in the playoffs.
The Castilla squad includes expensive teenagers such as Sergio Diaz, a €6 million Paraguay senior international, and €5m Uruguayan playmaker Federico Valverde, along with Greece under-21 striker Nikolaos Vergos and Austrian U21 defender Philipp Lienhart.
Other emerging stars have been sent on loan, including Marcos Llorente (Alaves), Borja Mayoral (Wolfsburg) and Martin Odegaard (Heerenveen).