Gary Johnson admits he will be searching for defender after Jamie McCombe suffered a suspected broken cheekbone in the 1-1 draw with Derby County.
The injury comes just days after City lost young Christian Ribeiro for a year with ACL damage, and Liam Fontaine aggravated an ankle problem.
World TV: Gary Johnson video interview
Speaking on Bristol City World after the Derby game, Gary said: "It's a sad situation when you see one of your players injured like that and when it's a broken bone, as it seems, it's normally six weeks out.
"Liam should be back on Monday but we probably will have to enter the transfer market to ensure we've got the numbers. We are short in terms of experienced centre-backs."
Nicky Maynard bagged his first league goal for City in the first half, but Paul Green's driven finish early in the second 45 earned a point for the visitors.
Gary said: "When you're one-nil up and then get brought back to draw the game 1-1 then you will be disappointed.
"We're a bit down because we think we've lost two points. We started very bright and everybody was up for it, both on and off the pitch.
"We should have come in (at half-time) two goals to the good. It was great for Nicky Maynard to get his first goal, but we wanted it to be a winner.
"We knew Derby weren't as bad as they looked in the first half. In the first 20 minutes of the second half we let them back into it. The goal was a comedy of errors.
"In the end it was anybody's game, but after two games we have four points - we'll learn from this game and move on."