Dempster admitted the January transfer window can’t open quickly enough as Stags slipped to 18th in League Two.
Dempster was given a pre-match boost by chairman John Radford last weekend when Radford's programme notes said they would not sack the manager as things stood.
But the players then limped to a tame 3-0 home defeat by Cheltenham Town to leave them six points off the bottom, and five games without a win, and Dempster said: “There needs to be change and January can't come quickly enough.
“It won't be major surgery but there will be changes – and there needs to be as we find ourselves in a very difficult predicament currently.
“Results haven't been good enough. Performances haven't been good enough and if we are going to start achieving our potential there has to be some changes in personnel, formation and tactics – all the different tweaks you can make to find that winning formula.”
Dempster had his players in for a rare Sunday morning session after Saturday's disappointment when a lot of home truths were spoken behind closed doors.
“They should have had a man sent off early on, but that's not why we lost the game 3-0,” said Dempster.
“I'm really disappointed with the goals we conceded – very weak.
“I had the players in training on Sunday morning and we spoke about it at length. There were some home truths and several of the senior players spoke very well about our current predicament.
“It all needs to be kept in-house but there was a lot of honesty. We will see what kind of a reaction we get this week in training. People are aware they need to start taking responsibility.”
He added: “I won't criticise individual players in public, making it personal. That's not my style. With that you want that respect back and, at times this season, the team performances don't reflect me as a person.
“The danger of taking responsibility for any of the negativity and poor performances is that lesser characters can hide behind you. It's important players don't hide behind me or things won't improve. We are all going through a difficult time.”