The Millers financial plight means all the money from the sale of Hoskins and Williamson to Premiership side Watford is needed to keep the club in business.
And without the pair the Yorkshire side rarely threatened against Chesterfield on Saturday.
Knill, a former Scunthorpe centre-back, admitted the home loss to the Spireites was the worst display of his side's season but knows he is limited in his bid to strengthen the Rotherham squad.
"There is no money to buy anyone so any signing will have to be on loan," he said.
"It's going to be tough but we just have to get on with it."