The Chilean also confirmed forward Marko Arnautovic is fit to play, while Andy Carroll and Jack Wilshere could also return to the side after recovering from long-term injuries.
Newcastle are on a three-game winning streak, though despite a recent poor run of form that has seen them win just once in their last seven matches across all competitions, Pellegrini is confident in the 'Hammers'.
Speaking ahead of the game, Pellegrini remarked: "For me, the pressure is always exactly the same. I never divide the games into game you can win or lose. I never think we can lose. We always try to win.
"It's important to have a strong mind, understand that every game in the Premier League is difficult.
"Of course it is not the same to play against Manchester City, Manchester United, Chelsea or the other big six teams, but our mentality is to understand that there are no weaker teams and we must try to play our best."
"Marko Arnautovic worked the whole week without any problems. One more day to recover. He is okay.
"Andy Carroll is one step forward than Jack Wilshere. He played 45 minutes in the friendly game against Brentford and in the last game [against Man City] he went to the bench. Both of them may be in the squad for tomorrow."