The Hammers lost their opening Premier League game 4-0 against Liverpool at Anfield last week, and will be looking to bounce back when they face Eddie Howe’s side at the London Stadium.
However, Manuel Pellegrini has suggested that the game may have come too soon for both Perez and Sanchez, and at best they could be in contention to make the bench.
“Carlos just arrived on the last day, he has worked just one week with us,” said Pellegrini to Football London.
“Lucas Perez is similar, we will see if they are at least able to come to the bench but I can not answer that question.”
Perez, 29, joined the Hammers on the transfer deadline day from Arsenal for a reported fee of £4 million. The Spaniard hasn’t had much of a pre-season and will require time to get back to full sharpness.
Sanchez joined the Hammers from Fiorentina on the final day of the transfer window, and has only trained with his new club for a week. The 32-year-old defensive midfielder could be in contention to make the bench but Pellegrini won’t risk him in the starting line up.