The former Barcelona, Real Madrid, Real Mallorca and Racing Santander player won the Uefa Cup with Sevilla in 2006.
He arrived in English football after being released by Real Mallorca last December, joining QPR in February.
Lopez opened talks after his three-month contract at Loftus Road expired but was unhappy with the wages being offered and the negotiations ended, leaving the player as a free agent.
It is understood he turned down offers from two other Championship clubs to join Swansea.
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