The midfielder was issued with a visa by the British Embassy in Paris yesterday and his registration was today approved by football's governing bodies.
Diop was due to arrive in the UK this afternoon and will be eligible to play in tomorrow's npower Championship fixture at home to Leicester City. However Lee Clark has already indicated that it's unlikely the 34-year-old will be handed a debut due to a lack of match fitness.
The former Senegal international's initial contract with Blues will run until 17 November and he has been handed first-team squad number 32.
On what his latest recruit will bring to the fold, the Blues boss told bcfc.com: "I feel we need some sort of physical presence in the middle of the pitch and I know him very well. I played alongside him for a while (at Fulham) and we were partners in the centre of the pitch and I know what he’s about.
"He’s competitive because of his size and his physique. He’s competitive in the air and on the floor but when he gets the ball down as well he can play. He’s obviously a threat in both boxes from set plays. I just felt that was one area as well where we were a little bit loose in a couple of games that we’ve lost."
On the unlikely prospect of seeing Diop in action this weekend, Clark added: "He can’t start because we had to release him last Thursday to go over to France to sort out the paperwork. I wanted to use this international break as a time to get some fitness into him but also put him in the development game (against Derby County) on Tuesday to see where he is in terms of match fitness but I couldn’t even do that to see whether he was right to start on Saturday.
"It would have been very similar to what I did with Paul Robinson. Paul obviously convinced me that he was ready and he’s since proved that he was ready and I wanted to do that with Bouba on Tuesday but he wasn’t available for that.
"The best case scenario with Bouba is that he will be on the bench. I spoke to him after the Huddersfield game and it was always in my plans to get to where he was in terms of fitness levels with him in my mind of being a starter against Leicester but that’s certainly ruled out now.
"Probably his last competitive game would have been sometime in March for West Ham so that would have been too big a risk."
A full, exclusive BluesTV interview with Diop will be on bcfc.com later today.