The Mexico worldwide scored just eight goals in 28 league appearances last season but is looking forward to working with Pellegrini.
The defensive-minded midfielder becomes the ninth player through the door at West Ham during a productive summer window for Manuel Pellegrini.
Perez was signed from Deportivo La Coruna for £17m in the summer of 2016 but failed to establish himself as a regular in the team.
Jose Mourinho Tells Officials That He Wants This Frenchman SOLD
Claude Puel's realistic aim will be to have Leicester finish in the top half of the Premier League this season. For example, Alexis Sanchez had a good pre-season with lots of matches and lots of minutes.
The 29-year-old, who spent last season on loan at Deportivo La Coruna, has signed a three-year deal with the Hammers.
Sanchez's future appears to be away from Fiorentina after spending last season on loan at La Liga side Espanyol. He scores goals, but can also create them and link well with the midfielders.
Wall Street sees funding hurdle to Musk's plan to take Tesla private
Most analysts were skeptical, but some said a deal could materialize if Musk succeeded in lining up the right funding. Public companies have four days to report certain material events that shareholders should know about to the U.S.
"From the very first meeting I had with Lucas, he made it very clear that he wanted to come to West Ham United and, for us, this is very important".
The Brazilian completed his medical on Friday and subsequently signed a four-year contract at London Stadium until 2022.
At least 43 killed, including children, in attack on Yemen market
Yemeni tribal leaders told the AP the Saudi-led US -backed coalition fighting Shiite Houthi rebels was behind the airstrike. The Iran-aligned Houthis regularly fire into Saudi Arabia and have targeted its capital, Riyadh , with ballistic missiles.