The 31-year-old defender, who had been a free agent since leaving Athletic Club Bilbao when his contract expired last summer, received an offer to join Albion after a trial with the club.
However, he has said he had no regrets about hanging up his boots: "I am doing this with a clear conscience, everything is decided and I am leaving football for good.
"I didn't want to try and fool anyone. I would have needed a month to get into shape and I didn't want to sign in those circumstances," he added.
