The former West Ham and Portsmouth powerhouse joined Blues on a one-month contract in mid-October, but is yet to make it off the bench for his first-team bow.
However, Diop, a free agent over the summer, is proving his fitness with every passing week for City's Under-21 side and followed up his goal against Sheffield United with another, amid a commanding performance, in the Development side's 2-0 win over Sheffield Wednesday earlier this week.
Asked whether he will be extending Diop's stay at St Andrew's, Clark said: "I'm considering it all the time. I'm watching how he is getting fitter and fitter, better and better. It's under consideration but we have other things that are priorities at the moment in terms of the games. He knows what I am about. We go back a long way.
"He got through the 90-odd minutes on Wednesday day and looks like he is getting fitter and stronger."
Clark added: "He's been very popular around the place. He hasn't entered the field of play yet but you see his demeanour around the place, he lifts everyone. After the games when we've had good results he's been so bubbly. He's been a massive boost for everybody. He is getting closer and closer to getting on the field."