Atletico Madrid flew flags at half-mast on Sunday in honour of former defender Jose Luis Capon and youth team player Christian Minchola.
Capon, who won Spanish league titles with Atletico in 1973 and 1977 and the 1976 Copa del Rey during a 10-year spell at the club, died at the age of 72.
His passing came just 24 hours after the death of 14-year-old Minchola – a member of the club's youth team.
"Today is a sad day for the rojiblanca family," the club said in a statement.
"Atletico de Madrid is in mourning for the death of our former player Jose Luis Capon Gonzalez. The former rojiblanco defender died at the age of 72 in his hometown.
"To remember Capon, the flag honouring our fans located in the Wanda Metropolitano will fly at half-mast for 24 hours in honour of our legendary player.
"With the departure of Capon, the Atletico family loses another of the symbols that gave everything for this club on and off the pitch. From the club, the president, chief executive officer and our board offer their sincere condolences to all his family and friends."
Commenting on the death of Minchola, the cause of which has not been revealed, head coach Diego Simeone said: "With all my heart I send my condolences to Christian's family and friends. Rest in peace."
Club captain Koke added: "Anger and pain for having to say goodbye to Christian Minchola. Life is very unfair.
"Proud that you wore this shirt. Much encouragement to colleagues, family and friends. Rest in peace."