The Baggies are on the verge of adding to their frontline this month as they close in on the signature of Diagne from the Turkish giants.
They have a deal in place with Galatasaray to sign the 29-year-old Senegal international on an initial loan deal with an option to buy.
Diagne underwent part of his medical in Turkey yesterday and West Brom are sorting out the final details of the deal ahead of securing his signature.
The forward is expected to be in England later today but Allardyce said that he wants to remain cautious until Diagne is signed and sealed as a West Brom player.
He is hopeful that the forward will add more goalscoring options to his squad as they look to survive in the Premier League this season.
The West Brom manager said in a press conference: “Hopefully if everything is OK, he will be arriving today.
“Not here yet. Until he walks through the door, I always speak with caution.
“Hopefully can give us more on the front line.”
Diagne scored nine goals in 15 Super Lig appearances for Galatasaray in the first half of the season.
