Diop chose the Hammers ahead of the likes of Borussia Dortmund last week.
He told L'Equipe: "I did not have a priority. The only criteria I had was that this club is counting on me. West Ham, it will be a club that will make me grow.
"The coach (Manuel Pellegrini) spoke to me, explained to me what he expected of me. I know that I will arrive in a big Championship, with very big players. It is a landing that I cross.
"After that, it's not an ending point. I did not play the C1, the World Cup. In football, I have not done anything yet."