The West Londoners have agreed an undisclosed fee with Spanish second-tier club Lugo for the 23-year-old.
Djalo, who signs a three-year deal with the option for another 12 months, also spent two years with Juventus but never appeared for their senior team.
The Spaniard told the club's official website: "The truth is, for me it is a proud moment. It's a big club, an emblem of the city, and for me it's a proud moment.
"Quite simply, I want to be here, I want to work here, I want to grow as a person and a footballer at this great club."
Djalo has also turned out for CF Badalona, Granada B, Girona and UCAM Mercia.