"I made a decision to come here because, first, it is the Premier League, second, it's a attractive club and the fans are always helping the club and, third, for me it's an awesome opportunity and an incredible project the club are leading, being ambitious and keen to achieve good things", said Sanchez.
Portuguese outlet A Bola, as quoted by Metro, is reporting that the north London side have deemed the 29-year-old to be surplus to requirements at The Emirates as Unai Emery prepares for his first season in charge at the club.
The Spain worldwide was signed by the Emirates club from Deportivo La Coruna for £17m in the summer of 2016.
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Perez joined Arsenal in August 2016 from Deportivo la Coruna but started just two Premier League games for the London club, making another nine appearances off the bench.
'I wish you all the best for the future and I hope you can go and achieve great things'.
West Ham director of football Mario Husillos, who added Perez's name to a list of signings that includes Yarmolenko, Ryan Fredericks, Lukasz Fabianski, Issa Diop, Jack Wilshere, Fabian Balbuena and Felipe Anderson, underlined the Spaniard's versatility.
"We welcome Lucas to West Ham United".
"There are other clubs interested but joining West Ham would allow him to continue in London and in the Premier League and Lucas wants to continue in London".