The Dutch striker hasn't netted from open play in the league this season.
"The important thing is how you react to that and I've got no doubt Dirk will keep on working hard and getting himself in positions to score. And if he carries on doing that then I'm sure the goals will flow.
"There's no point picking on individuals when we don't win. We win as a team, we draw as a team and we lose as a team, and that's all there is to it."