Costly has failed to score in his eight Birmingham appearances
Birmingham boss Alex McLeish believes his strikers need to start firing if they are to secure promotion to the Premier League.
Blues, with just 44 goals, have scored the fewest of the top ten Championship sides.
"I feel that the lads have goals in them, and while there's eight games to go there's time," McLeish told BBC WM.
"Carlos Costly could have had four goals since he's come here, but he's not, and it's a problem for us."
Honduran international Costly, 26, is starting to show signs of settling in at St Andrew's, making his third start in Tuesday's draw at Barnsley following his January loan move from Polish club Belchatow.
Carlos could have had four goals since he's come here, but he's not, and it's a problem for us
Birmingham boss Alex McLeish
"I thought Costly did well again, he was keeping the ball and I think the fans will like him because of his willingness to close down everything," McLeish noted.
The Blues boss has been hamstrung by a host of injuries in the strike department, and although Garry O'Connor was back on the bench at Oakwell after four months out, McLeish is still waiting on the fitness of James McFadden, Marcus Bent and top scorer Kevin Phillips.
"Kevin's now stepped up training, clinically at a good level," said the former Rangers and Scotland manager.
"You can scan him again all you like, and in three or four weeks he'll still have a bit of fluid there.
"But Kevin knows his own body and he's now at a level where he's stepping things up. I doubt if he'll be ready for the weekend, but almost certainly for the Norwich game."
That means Costly and England under-21 international Cameron Jerome will again be paired together for this weekend's trip to Doncaster, with O'Connor retained on the bench.
Birmingham may also be without Lee Bowyer again - the on-loan West Ham midfielder is due to see a specialist about the groin and back problem that kept him out of the game at Barnsley.
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