Cash-strapped Rotherham - who started the season with a 10 point deduction after going into administration over the summer - agreed a transfer fee with the Tykes on Monday, just days after manager Alan Knill warned there was no money to spend on permanent signings.
The Yorkshire side had already secured the loan signings of Ian Henderson and Tiggy Diagouraga earlier in the current transfer window.
And Knill is expected to add to his squad further with loan signings before the month is out.