The club from the working class district of Vallecas to the south east of Madrid's city centre beat title rivals Real Betis to go top of the second division on Sunday, a month after their owners filed to go into administration.
Rayo's majority shareholder Jose Maria Ruiz-Mateos last month applied for his Nueva Rumasa business to be protected from its creditors in 10 of its divisions, including the cash-strapped club which has debts of around 22 million euros on a budget of 18 million.
Ruiz-Mateos spent time in prison for tax evasion during the 1980s after the government was forced to step in and take over his previous business empire when they ran into financial difficulties.
Rayo's predicament is far from unique to Spanish football though their staff are perhaps the worst off out of all the teams in the top two divisions.
Sunday's visitors Betis are already in administration, and third-placed Celta Vigo have just come out of it, while top-flight Real Mallorca were barred from playing in the Europa League this season after taking a similar course of action.
Last week, Rayo's team captain Michel had explained the situation at their nearby training ground, where a handful of fans and reporters hung around the dressing room door in a manner that would be unthinkable up the road at Real Madrid City, the largest sports complex ever built by a football club.
"The economic problems affect the team," the 35-year-old midfielder told Reuters, "but we have to focus on the sporting side of things and hope there is a rapid solution to it all.
"We are owed money from last season. We have received some money, it is different for each player, but they still owe us money from last year. The club are looking to be able to do something for us as soon as possible."
Michel came up through the Rayo youth ranks and is a veteran of the side that achieved the club's highest ever finish of ninth in La Liga in 2000 which qualified them for the UEFA Cup under former Real Madrid and Tottenham Hotspur boss Juande Ramos.
They eventually fell to fellow Spaniards Alaves in the quarter-finals of their first European campaign, the Basque club going on to lose to Liverpool in the 2001 final.
He clearly identifies with the club's fans who have given their backing to the squad and staff, even organizing some collections.
The fans have directed their anger at club president Teresa Rivero, the wife of Ruiz-Mateos, calling for her and the family to leave after 18 years at the helm. The petitions for her to go grew after she suggested the players were not really interested in promotion following an earlier protest by the squad, though she later apologised for her comments.
"The fans are also worried because of the situation with the club," Michel added. "Given that we are in the fight to win promotion, they also want to see the light or hear something new, so that they know the players are only thinking about sporting affairs.
"The fans have shown their support for the team, and their unhappiness
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