He confirmed the Reds have knocked back bids for the defender this week, with Wolves and Sunderland leading the race.
Heckingbottom is also eyeing new recruits, with Wigan midfielder Sam Morsy and Chesterfield winger Gboly Ariyibi among his targets.
The Reds saw a bid rejected for Ariyibi earlier this week, with Spireites boss Danny Wilson labelling the offer as “derisory”, with the clubs’ valuations of the player currently way apart.
Still confident of activity, Heckingbottom said: “It will be busy.
“We know we are light as a squad and definitely need help and reinforcements.”
On the current situation with Mawson, he added: “If Patrick (Cryne) had come to me and said, ‘It is ‘x’ amount and it gets done’, you know he would go on that.
“But he has not said that and he might still be here yet.”
Meanwhile, the Reds have confirmed that Sessi D’Almeida will be out for the season with a cruciate ligament injury, although Sam Winnall is back for the weekend derby with Rotherham.
Huddersfield Town head coach David Wagner says he is not planning any further signings after the capture of Tareiq Holmes-Dennis and only envisages it changing if someone moves on.
The future of Kyle Dempsey remains unclear, with Wagner admitting there is interest after the player was allowed to speak with other clubs about a loan move.
Wagner said: “I am done and am not active. But if I have to react like I had to when Jason (Davidson) came and said he wanted to leave, then I have to be prepared.
“I will make the final decision (on Dempsey) after the Wolves game on if we will let him go out on loan.”