The dispute centres on a transfer fee from August 2022 for the 24-year-old forward, who made a move to the club.
Flamengo claims that Almería has failed to meet its financial obligations for nearly 600 days, resulting in a debt of approximately €1.8 million.
Flamengo have also faulted Ronaldo's involvement in the club's financial transaction leading to the debt.
Ronaldo's club in debt
In an official statement, Flamengo also highlighted Cristiano Ronaldo's recent acquisition of a stake in the Spanish side.
In a strongly worded announcement, the Rio de Janeiro-based club did not mince words.
"Almería has been in default for 590 days and has accumulated an estimated debt of over 1.8 million euros, thereby shamelessly disregarding agreements made and the rules of international football," the statement read.
Flamengo also pointed to Cristiano Ronaldo's recent business dealings, noting, "In February, Cristiano Ronaldo acquired 25% of the Spanish club."
This inclusion suggests the Brazilian club holds the new co-owner partially accountable for resolving the matter.
According to Flamengo, FIFA has already acknowledged the debt, but Almería has allegedly continued to refuse payment.
As a result, the Brazilian club has announced its intention to escalate the issue by taking the case to the Court of Arbitration for Sport (CAS), expressing confidence that the governing body will take appropriate action.
Ronaldo's investment in Almería was driven by a long-held desire to contribute to football from an administrative role.