Rubio has showered praise on Livingston despite leaving the Scottish Premier League club to return to Spain.
Oscar Rubio is expected to play in Spain next season
The 28-year-old defender is leaving following the arrival of Paul Lambert as manager during the summer.
"I have to say that these last four years have been the most enjoyable of my entire football career," said Rubio.
"Livingston will always have a special place in my heart and I will never forget the good times I spent here with the staff and the supporters."
Rubio, who was known by his nickname instead of his given name, Oscar Montalban Ramos, joined from Portuguese side Farense in 2001.
He helped Livi lift the CIS Insurance Cup last year and also netted the club's first European goal, against Liechtenstein side FC Vaduz in the Uefa Cup in August 2002.
Rubio, who made 142 starts and and came on six times as a substitute, is second only to David Bingham in terms of club appearances.
Chief executive Vivien Kyles, who expects Rubio to return to Spanish football next season, said: "Oscar has been a popular figure with staff, team-mates and supporters at Livingston during the last four years.
"He was an important member of the side as it consolidated its position after a promotion to the SPL a few years ago and we wish him all the best for the future."
Meanwhile, French midfielder Franck-Augustin Dia will join Belgian defender Harald Pinxten at Livingston for a trial on Monday.
The 27-year-old Pinxten, presently with Antwerp, is already at Almondvale and could win himself a two-year deal.
Dia, a 26-year-old born in the Ivory Coast whose contract with French Second Division side Angers has expired, will train with the squad before joining their Italian training camp.
Livingston are also reportedly interested in Shamrock Rovers' transfer-listed midfielder, Patrick McCourt, who has previously been linked with Bristol City and Motherwell.