But Allardyce is convinced that the young Croatian will come good sooner rather than later.
"We've been bringing him in slowly, we know what we see in training, he creates and scores goals and his technique is very good," Allardyce told the Rovers website.
"Unfortunately he's probably just a little nervous at the minute trying to search for his first Premier League goal.
"That should have been at Manchester United but had he not had that taken away from him by an outrageous decision by the assistant referee, he may have scored four or five by now.
"He'll be disappointed that he didn't win us the game against Hull City, but I am really pleased that he is getting the chances, that is very very important because I think eventually they will start going in."