Despite this his manager Alan Curbishley insists the striker has done well to get where he currently is and given time will find his best form.
Curbs told the official site, "He has done well to get where he is, it was a big injury, he has worked ever so hard at it.
"Sometimes players can be affected by team selection, can be affected by the way the team's playing, results, scoring goals.
"This year, he came in roughly after the first couple of games, played three or four. Then he hurt his knee up at Aston Villa and missed five or six weeks. I don't think I have done such a bad job in terms of bringing him back and easing him in.
"We have all got to get on with it. I have one or two players there who are not quite happy with what they have produced and we just have to roll our sleeves up for the next game."