He told the club's official website: "We have done well over the last two or three years to bring in the right quality of players at the right price and they have always performed for us.
"However, it becomes harder and harder because when we flag players up, other clubs take note and understand that if we are interested then they must be good players.
"That is a new factor we have to cope with now. We will keep working hard and do the best with what we have got.
"We are viewed certainly as one of the clubs just outside the top four or five that top players will contemplate signing for and that is important when it comes to recruitment.
"We need a little bit more investment this year than possibly we have done in recent years to make sure that we keep going in the right direction."