Nigel Clough says a number of tough decisions have had to be made already this summer, as the Blades boss reflected on the retained list which was announced earlier this month.
The Gaffer remarked: "It was difficult deciding on the futures of Matt Hill and Shaun Miller, with regards to Shaun we couldn't wait and gamble on his form or fitness, we have to hit the ground running in pre-season and we can't afford any ifs or buts next season.
"Chris (Porter) is considering the offer we have made him, it is probably lower than he would have liked, but we have to think about what is best for the the Club.
"We are speaking to Febian (Brandy) and Lyle (Taylor), but it is fair to say they would probably be available should the right offer come in for either of them.
"We want a competitive squad of 18 or 19, Terry Kennedy will be just outside that and predominantly an U21 player, so we have scope for further additions."
Clough concluded by saying contract talks with influential defender Harry Maguire are taking place, the manager added:
"Talks are continuing with Harry and his representatives. We always said we would pick things up in the summer once the season had finished.
"Harry still has a year left on his current deal, so if an offer comes in for him we would consider it, but it would have to have the best interests of the Club at heart."