The defender urged Valencia to allow him to move to Camp Nou and his wish now appears to have been granted after weeks of negotiations
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The two clubs have been locked in negotiations for several weeks, with the Catalans eventually confirming their interest in the player after lodging an opening bid July 16.
That offer was rejected as Valencia demanded Barca match the player's release clause, which stands at 20 million euro, before the player reportedly pleaded with his current employers to sanction a move to Camp Nou.
The 30-year-old's wish has now apparently been granted after the two sides agreed a fee believed to be close to Valencia's asking price, and he could even be unveiled as a Barcelona player Tuesday.
Mathieu is set to head to Catalonia as the rest of his soon-to-be-former teammates at Valencia head to South America for a preseason tour Wednesday.
The Frenchman would become Barcelona's fifth signing of the summer following the arrivals of Marc-Andre ter Stegen, Claudio Bravo, Ivan Rakitic and Luis Suarez.
The move would bolster a back line left depleted by the retirement of Carles Puyol at the end of the season, with Mathieu set to battle it out for a place alongside Gerard Pique at the heart of the back four.