Prieto came through the youth system at the Basque side and, after making his debut in 2003, has gone on to play 530 games for the first team.
“Xabi Prieto will hang up his boots at the end of the season,” a Real Sociedad statement read on Tuesday.
The 34-year-old one-club man is fifth in the San Sebastian side’s list of all-time leading appearance makers.
“Your class on and off the pitch will be etched forever in the memory of the Real Sociedad family,” added the club’s statement.
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