The 24-year-old was expected to complete his move to the KC Stadium on Monday night before he failed a medical, prompting Bruce to renew his search.
He told talkSPORT: "We are obviously looking because we are all disappointed at what happened with Charlie.
"We will go back to the drawing board again and see, and I would expect us to still bring in two or three at least to try to give us a hand. We have brought in three at the moment - I would expect us to bring in another three at least to help us over the next 10 months.
"But as I said, we are going to go back to the drawing board now because there has been a lot of work on Charlie and I think he would have been great for us, but unfortunately, it doesn't look as if it's going to be."
The details of Austin's medical have not been made public, although the frontman has struggled with shoulder problems over the years.
Bruce said: "There has been a bit of a problem with his medical, which is the worst scenario for everybody concerned, and more so the boy.
"It's an awful, awful, awful situation to find ourselves in, but unfortunately the medical is not great, so it looks as if it is a non-starter at the moment.
"I think he is surprised because he has not really missed any games over the last couple of years.
"It is a blow for him and it's a blow for us, but there you go. These medicals are so stringent, things have progressed with scans and all the rest of it and obviously he has got a problem."
Source: PA
Source: PA