Barrera, 25, signed for West Ham United in 2010 after a strong World Cup in South Africa that endeared him to talent scouts across Europe. After a season mostly on the bench, he was loaned out to Zaragoza for the 2011-12.
In Spain, Barrera joined fellow Mexicans Efrain Juarez and manager Javier Aguirre on a team that narrowly avoided relegation. Pablo played in 20 games for Los Maños.
With Barrera's signing, Cruz Azul caps off an active summer of international signings, as La Maquina had previously added Argentine striker Mariano Pavone as well as Colombian defender Luis Perea.
A product of crosstown rival UNAM, Barrera played in 85 matches for Pumas between 2005 and 2010, scoring 18 goals in the process before making the European jump.
Barrera has found extended success with the Mexican national team, scoring six goals in 49 matches.
Financial terms of the deal were not disclosed. Barrera signed for West Ham in 2010 for 4 million pounds.
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